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BULLETIN   OF   THE   GEOGRAPHIC   SOCIETY   OF    CHICAGO. 
NO.  1. 


THE  GEOGRAPHY 


OF 


CHICAGO  AND  ITS  ENVIRONS 


BY 


ROLLIN  D.  SALISBURY 

AND 

WILLIAM  C.  ALDEN 


CHICAGO 

Published  by  the  Geographic  Society  of  Chicago 

1899 


PREFATORY  NOTE. 

It  is  the  purpose  of  this  essay  to  present  an  outline  of  the 
geography  of  Chicago  and  its  immediate  surroundings,  and  espe- 
cially to  sketch  in  as  simple  a  manner  as  possible  the  course  of 
events  by  which  that  geography  was  developed.  The  essay  is  not 
intended  to  take  the  place  of  the  detailed  descriptions  of  special 
localities  heretofore  published  or  yet  to  be  published.  Rather  is 
it  meant  to  give  such  an  account  of  the  region  about  the  city  that 
the  interpretation  of  local  phenomena  may  be  more  easily  and 
more  generally  understood. 

The  detailed  field  work  on  which  the  essay  is  based  was  done 
by  the  junior  author,  who  furnished  the  data  for  the  maps,  and 
made  the  first  draft  of  the  essay.  Acknowledgment  is  also  made 
of  indebtedness  to  the  work  of  earlier  students,  whose  names  are 
mentioned  in  the  course  of  the  essay. 

In  the  preparation  of  the  illustrations,  valuable  assistance 
has  been  given  by  Mr.  Wallace  W.  Atwood,  Mr.  Frank  H.  Harms, 
Dr.  Henry  C.  Cowles  and  Miss  Evelyn  Matz.  The  Frontispiece 
is  from  a  model  made  by  Mr.  C.  E.  Siebenthal. 


SI 


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'^  OUTLINE. 

^'  THE  CHICAGO  PLAIN. 

Topography, 
yQ  General  Topographic  Relations. 

_^  Topography  of  the  Plain. 

1^  Structure  of  the  Plain. 

L*  Relations  of  Rock  and  Drift. 

^  The  Rock. 

The  Drift. 
"^  Unstratified  Drift. 

Stratified  Drift. 

Surface  of  the  Rock  Beneath  the  Drift. 
The  Drift  is  of  Glacial  Origin. 


DEVELOPMENT  OF  THE  PRESENT  GEOGRAPHY. 

The  Geography  of  the  Rock  Surface. 

The  Glacial  Period. 

Development  of  the  Ice  Sheet.  ^ 

The  Erosion  Work  of  the  Ice.  * 

Deposits  Made  by  the  Ice. 

Lake  Chicago. 
Origin. 

The  Chicago  Outlet. 
Stages. 

The  Beaches  of  Lake  Chicago. 

The  Upper  or  Glenwood  Beach. 

The  Oak  Park  Spit. 

Cliff  and  Wave-Cut  Terrace. 

Dunes  on  the  Glenwood  Beach. 

The  Glenwood  Spit. 

Duration  of  the  Glenwood  Stage. 

Changes  of  Water  Level. 

Life. 

Blue  Island. 

Interval  of  Emergence. 

The  Calumet  Beach. 

Rose  Hill  Bar. 

Evidence  of  Life  in  the  Lacustrine  Deposits  of  the  Calumet  Stage 

The  Third  or  Tolleston  Beach. 

Stony  Island. 

Evidences  of  Life  at  the  Tolleston  Stage. 

Changes  in  Topography  Effected  by  Lake  Chicago. 
Recent  Changes. 

Lake  Michigan  Beach. 

The  Ddnes. 

Stream  Erosion. 

Weathering. 

The  Formation  of  the  Soil. 


I. 
THE  CHICAGO  PLAIN. 

TOPOGRAPHY. 

General  topographic  relations. — The  topography  of  a  region  is 
always  significant  of  its  history.  The  City  of  Chicago  is  situated 
on  a  low,  strikingly  flat  plain,  bordering  the  west  side  of  the  head 
of  Lake  Michigan.  The  limits  of  the  plain  for  a  tract  about  the 
city  are  shown  in  Fig.  i  (see  also  Frontispiece),  from  which  it 
will  be  seen  that  the  plain  is  roughly  crescentic.  Its  inner  border 
is  formed  by  the  shore  of  Lake  Michigan,  while  its  outer  margin, 
marked  by  higher  land  (shaded  in  Fig.  i),  extends  from  Wyinetka 
on  the  north,  through  Galewood  and  La  Grange  on  the  west,  to 
Glenwood  and  Dyer  (Indiana)  on  the  southwest  and  south.  Its 
greatest  width  is  about  15  miles  in  a  direction  southwest  from 
the  city. 

From  the  shore  of  the  lake,  the  level  of  which  is  about  581 
feet  above  mean  tide  level  in  New  York  Harbor,  the  Chicago  plain 
rises  very  gradually  to  a  nearly  uniform  height  about  60  feet 
above  the  lake.  At  this  level,  the  flatness  of  the  plain  is  inter- 
rupted, and  to  the  west  and  south  the  surface  rises  promptly,  and 
its  topography  is  rolling.  The  rise  is  continued  until  the  rolling 
surface  reaches  an  extreme  altitude  of  200  feet  above  the  lake. 
From  this  considerable  elevation  there  is  a  decline  toward  the 
west,  southwest  and  south.  In  other  words,  the  Chicago  plain  is 
shut  in  by  a  broad,  ridge-like  belt  of  gently  rolling  topography. 
Observations  beyond  the  immediate  vicinity  of  Chicago  show  that 
this  ridge-belt  comes  down  from  the  north  and  swings  about  the 
head  of  the  lake  basin.  It  is  in  reality  a  glacial  moraine,  and  has 
been  called  the  Valparaiso  moraine  from  the  city  of  Valparaiso 
(Indiana),  which  is  situated  upon  it.  Where  crossed  by  the 
Wabash  Railroad  southwest  of  Palos  Springs  (Plate  II),  this 
moraine  has  a  width  of  15  miles,  its  outer  edge  being  at  New 
Lenox.      These   relations   are   shown   on  the  accompanying  maps 

5 


6  THE  GEOGRAPHY  OE 

(especially  PI.  II),  to  which  constant  reference  should  be  made. 
North  of  the  line  of  the  Chicago,  Burlington  &  Quincy  Railroad 
the  moraine  is  ill-defined,  and  the  location  of  its  eastern  border  is 
somewhat  arbitrar\'. 


Fig.  I.— The  Chicago  plain  and  its  surroundings. 

Cutting  directly  across  this  low  broad  ridge  in  a  southwesterly 
direction,  from  Summit  to  Lemont,  is  the  valley  now  traversed  by 
the  Des  Plaines  river,  the  Illinois-Michigan  canal,  and  the  new 
Drainage  Canal.   This  valley  has  abrupt  slopes,  varies  in  width  from 


CHIC  A  GO  AND  ITS  EN  VI R  ONS.  7 

one-half  mile  to  one  and  one-fourth  miles,  and  is  30  to  100  feet  deep. 
From  side  to  side,  the  floor  of  this  valley  is  nearly  flat.  At  its  lake- 
ward  end,  the  bottom  is  continuous  with  the  Chicago  plain,  and  is 
less  than  15  feet  above  the  level  of  the  water  in  the  lake.  These 
relations  are  shown  in  the  Frontispiece,  PI.  II  and  in  Fig.  i. 
From  Summit  to  Lemont,  the  fall  is  so  slight  as  to  be  spoken  of 
as  "the  twelve-mile  level." 

Tributary  to  this  valley  at  Sag  Station,  about  three  and  one- 
half  miles  above  Lemont,  is  a  second  valley  of  like  dimensions 
known  as  "the  Sag."  This  valley  runs  nearly  due  west  from  the 
village  of  Worth  on  the  Wabash  Railway,  to  Sag  Station  on  the 
Chicago  &  Alton  Railway.  It  is  traversed  by  a  small  creek  known 
as  the  Canal  Feeder.  These  valleys  converge  and  unite  at  Sag 
Station,  including  between  them  a  triangular  tract  of  elevated  land 
of  undulating  topography.  This  isolated  area,  known  as  Mount 
Forest,  has  a  length  of  six  miles  and  a  width  of  four. 

The  floor  of  the  Sag,  as  well  as  that  of  the  Des  Plaines  valley, 
is  continuous  with  the  Chicago  plain.  These  two  valleys,  there- 
fore, give  ample  outlet  for  drainage  from  the  Chicago  plain  «outh- 
westward  across  the  moraine  belt,  and  thence  by  way  of  the  Illinois 
and  Mississippi  rivers  to  the  Gulf  of  Mexico.  Following  the  line 
of  the  canal,  there  is  a  rise  of  less  than  15  feet  from  the  present 
level  of  the  lake  to  the  divide  which  separates  it  from  the  Des 
Plaines  river.  The  lake,  therefore,  barely  escapes  drainage  into 
the  Mississippi  river  system,  even  without  the  new  canal. 

Topography  of  the  plain. — Apart  from  the  Mount  Forest  island 
already  mentioned,  the  most  prominent  topographic  feature  of  the 
plain  is  the  Blue  Island  ridge  (PI.  II),  seven  miles  west  of  the  lake 
at  South  Chicago,  This  ridge  runs  nearly  due  north  and  south, 
having  a  length  of  six  miles,  a  width  of  about  one  mile,  and  an 
elevation  of  25  to  50  feet  above  the  surrounding  flat. 

Just  west  of  South  Chicago,  between  the  Blue  Island  ridge 
and  the  lake,  is  a  minor  elevation  of  rock  known  as  Stony  Island, 
(S.  I.  PI.  II).  Its  longer  axis  has  an  east-west  direction.  The 
length  of  the  "island"  is  one  and  one-fourth  miles,  its  width 
about  half  a  mile,  and  its  height  about  20  feet  above  its  marshy 
surroundings. 

Traversing  the  plain,  and  converging  to  the  two  southwestward 
valley-extensions  of  the  plain  on  either  side  of   Mount   Forest,  are 


THE  GF.OGRAJ'IIY  OF 


77«;  YK  7/ioevmi 


a  series  of  low  ridges  of  sand  and  gravel  so  related  to  the 
lake,  to  the  valleys  on  either  side  of  Mount  Forest,  and 
to  one  another,  both  in  elevation  and  arrangement,  as 
to  be  most  significant  in  working  out  the  geographic  his- 
tory of  the  region.  In  many  parts  of  the  city  where  the 
natural  surface  has  not  been  destroyed  by  grading,  as 
well  as  at  many  points  outside  the  city,  these  low  ridges 
are  brought  into  prominence  by  the  trees  which  grow 
upon  them,  while  their  surroundings  are  treeless.  Some 
of  these  inconspicuous  ridges  are  shown  on  PI.  II. 

Apart  from  these  features,  some  of  which  are  not  pro- 
nounced, the  notable  characteristic  of  the  topography 
of  the  plain  is  its  flatness. 


STRUCTURE  OF  THE  PLAIN. 

Relations  of  rock  and  drift. — The  sub-structure  of  the 
Chicago  plain  is  solid  rock.  This  may  be  seen  in  the 
several  quarries  about  the  city,  arfd  is  made  known  by 
deep  borings  and  excavations  of  other  sorts  at  many 
points  where  the  rock  is  not  exposed  at  the  surface. 

Overlying  the  bed-rock  is  a  mantle  of  unconsolidated 
material  composed  of  bowlders,  clay  and  sand,  and 
known  as  drift.  Borings  for  wells,  excavations  for  the 
foundations  of  buildings,  and  the  exposures  of  rock  in 
the  quarries,  show  that  the  thickness  of  the  drift  mantle 
is  extremely  variable,  and  since  the  surface  of  the  plain 
is  nearly  flat,  it  follows  that  the  surface  of  the  rock  on 
which  the  drift  rests  must  be  very  uneven  (Fig.  2).  If 
the  drift  mantle  were  to  be  stripped  off,  there  would 
remain,  instead  of  the  flat  plain  on  which  the  city  now 
stands,  a  markedly  uneven  surface.  The  present  rock 
outcrops,  where  the  drift  is  thin  or  absent,  would  be 
the  tops  of  hills  rising  above  their  surroundings,  that  is, 
above  the  plain  where  the  drift  is  now  thick.  The  slopes 
from  the  hilltops  to  the  valleys  about  them  would  be 
sometimes   steep  and  sometimes    gentle.        While    city 


^rSm^o^c^knon  engineer,    Mr.  Samuel  G.  Artingstall  prepared  a  map  of 
caj)""""  *"'''"  the    city  giving    the  elevation  of    the   rock    surface    at 


CHICAGO  AND  ITS  ENVIRONS.  9 

various  points,  as  shown  by  borings.  While  the  data  for  this 
map  were  insufficient  to  determine  the  details  of  the  topog- 
raphy of  the  rock,  the  map  showed  clearly  the  undulatory 
character  of  its  surface,  and  the  consequent  varying  thickness  of 
the  drift,  not  only  in  the  plain,  but  also  over  the  area  beyond  the 
plain,  where  the  drift  surface  is  undulatory. 

The  lowest  level  of  the  rock  surface  determined  is  near  the 
North  Branch  of  the  Chicago  river,  about  one-half  mile  north  of 
its  junction  with  the  South  Branch.  The  surface  of  the  rock  is 
here  124  feet  below  the  level  of  Lake  Michigan.  Passing  out 
radially  from  this  point  the  rock  surface  rises,  with  many  undula- 
tions, and  numerous  exposures  at  the  surface.  This  rise  in  the 
surface  of  the  rock  is  continued  under  the  moraine  surrounding 
the  Chicago  plain,  until  it  reaches  an  elevation  of  100  to  no  feet 
above  the  lake  level. 

While  the  rock  surface  is  higher  outside  the  Chicago  plain 
than  under  it,  thd  greater  elevation  of  the  surrounding  country 
is  not  due  entirely  to  this  cause.  From  the  study  of  one  hun- 
dred borings  distributed  over  the  plain,  it  has  been  esti|?iated 
that  the  average  elevation  of  the  rock  surface  under  the  plain  is 
45  to  50  feet  below  the  level  of  the  lake.  From  about  sixty  bor- 
ings west  and  southwest  of  the  plain  in  the  area  of  higher  land 
with  rolling  topography,  the  average  elevation  of  the  rock  under 
the  moraine-covered  territory,  has  been  estimated  to  be  25  to  30 
feet  above  the  level  of  the  lake.  This  gives  a  difference  of  70  to 
80  feet.  In  the  plain  the  drift  varies  from  o  to  130  feet  in  thick- 
ness, with  an  estimated  average  of  50  feet.  In  the  moraine  belt, 
the  average  thickness  of  the  drift  has  been  estimated  at  150  feet. 
It  is  thus  evident  that  the  belt  of  higher  land  above  the  Chicago 
plain  is  due  partly  to  a  rise  in  the  surface  of  the  rock  beneath 
it,  and  partly  to  the  greater  thickness  of  the  drift  (Fig.  2). 

The  rock. — The  rock  which  underlies  the  plain  about  Chicago 
is  limestone.  At  the  various  quarries,  and  wherever  the  rock  is 
exposed,  it  may  be  seen  to  contain  bits,  or  sometimes  even  large 
masses  of  coral,  fragments  of  crinoid  stems,  and  fragmentary  or 
perfect  shells  of  various  forms  of  shell-bearing  life.  Locally,  the 
limestone  may  almost  be  said  to  be  made  of  such  fragments. 
These  fossils  give  positive  evidence  of  the  origin  of  the  limestone, 
for  all  of  them  are  the  relics  of  life  which  lived  in  sea  water.      In 


10  THE  GEOGRAPHY  OE 

the  ocean  to-day  similar  accumulations  of  coral  and  shells  are 
making,  where  the  conditions  are  favorable.  Geologists  are 
therefore  confident  that  the  limestone  of  this  region  was  accumu- 
lated beneath  the  sea,  and  this  means  that  the  ocean  covered  the 
site  of  our  city  when  the  limestone  was  formed. 

By  means  of  its  fossils,  and  by  other  means  less  readily 
explained,  the  age  of  the  limestone,  in  terms  of  geological  chro- 
nology, is  known.  It  belongs  to  the  later  part  of  the  Silurian 
period,  and  the  Silurian  is  the  third  of  the  six  or  seven  long  per- 
iods which  make  up  the  Paleozoic  era,  the  first  era  when,  so  far 
as  now  known,  there  was  abundant  marine  life.  The  local  rock 
is  known  as  the  Niagara  /irnesio?ie,  because  it  is  believed  to  be  of 
the  same  age  as  the  limestone  at  Niagara  Falls,  and  the  limestone 
at  that  point  was  long  since  named  Niagara. 

The  limestone  may  be  seen  at  all  the  quarries  about  the  city. 
The  best  exposures  are  at  or  near  Stony  Island,  Hawthorne,  Bridge- 
port, Elmhurst  and  Lyons. 

Until  recently  no  formation  of  rock  (barring  the  drift)  younger 
than  the  Niagara  was  known  in  the  immediate  vicinity  of  Chicago. 
But  recently  Mr.  Stuart  Weller  has  found  remnants  of  a  forma- 
tion of  the  Devonian  period  (the  period  next  following  the  Silu- 
rian) at  the  quarry  a  mile  west  of  Elmhurst.  Meagre  as  these 
remnants,  are  they  show  that  beds  of  Devonian  age  once  overlay 
the  Niagara  limestone.  Like  the  Niagara  formation,  these  Devon- 
ian remnants  are  of  marine  origin,  and  prove  the  existence  of 
the  sea  in  this  region  in  the  Devonian,  as  well  as  in  the  Silurian 
period.  The  waters  of  the-  Silurian  and  Devonian  seas  in  this 
region  were  probably  not  deep.  Their  shallowness  is  suggested 
by  the  character  of  the  fossils.  For  example,  corals  do  not 
flourish  in  deep  waters,  and  corals  are  abundant  in  the  Niagara 
limestone.  It  is  possible  that  still  younger  beds  (the  Carbonifer- 
ous) once  overlay  the  Devonian,  but  if  so,  there  is  now  no  con- 
clusive evidence  of  the  fact. 


THE  DRIFT. 

Good  exposures  of  the  drift  may  be  seen  along  the  lake  bluff 
from  Evanston  northward,  along  the  line  of  the  new  drainage 
canal,  from  Bridgeport  southwestward  to  Lemont,  and  at  the  clay 


CHICAGO  AND  ITS  ENVIRONS.  ii 

pits  of  the  various  brick-yards  of  the  city  and  its  surroundings. 
Some  of  these  pits,  accessible  from  various  parts  of  the  city,  are 
the  following:  Near  the  North  Branch  of  the  Chicago  river,  west 
of  Lincoln  Park;  in  the  vicinity  of  South  Robey  and  Forty-third 
streets;  west  of  the  Union  Stock  Yards;  at  Purington  Station  on 
the  Chicago,  Rock  Island  and  Pacific  railway. 


Fig.  3.    Glacial  drift  or  till.     A  typical  section.     (Atwood.) 

Apart  from  these  exposures  which  are  more  or  less  perma- 
nent, temporary  exposures  are  frequently  to  be  seen  at  various 
points  in  the  city  where  excavations  are  being  made  for  the  foun- 
dations of  buildings,  for  water-pipes,  gas-pipes,  etc. 

Unstratified  drift.  The  drift  at  various  points  presents  various 
characteristics.      In  most  of  the  localities  where  the  more  perma- 


12  THE  GEOGRAPHY  OF 

ncnt  exposures  occur,  the  drift  consists  of  a  matrix  of  dense  blue 
(in  places  buffish)  clay,  in  which  are  imbedded  many  stones  (Figs. 
3  and  4).  In  size  the  stones  range  from  pebbles  to  bowlders  sev- 
eral feet  in  diameter.  The  material  is  in  general  without  arrange- 
ment; that  is,  the  fine  and  the  coarse  are  intimately  mingled.  To 
put  the  matter  in  another  way,  the  drift  does  not  show  the  assort- 
ment and  stratification  characteristic  of  deposits  made  by  water. 
Much  of  the  stony  material  is  too  coarse  to  have  been  handled 
by  waves  or  currents  of  any  ordinary  strength. 


Flc.  4.     Till  in  the  lake  blurt"  south  of  Winnetka.     Beach  gravel  in  the  forcRrouud.     (Harms.) 

The  greater  part  of  the  stony  material  of  the  drift  was 
derived  from  the  Niagara  limestone  which  underlies  the  drift,  not 
only  about  Chicago,  but  throughout  northeastern  Illinois  and  east- 
ern Wisconsin  as  well.  Another,  but  smaller  portion  of  the  stones 
of  the  drift  are  fragments  of  sedimentary  rock  from  other  forma- 
tions, while  still  another  part  are  fragments  of  metamorphic  and 
igneous  rock.  More  commonly  than  otherwise  the  larger  bowl- 
ders belong  to  this  last  class,  and  the  formations  from  which 
they  came  are  found  about  Lakes  Superior  and  Huron,  and  other 
points  to  the  north  and  northeast. 

If  the    stones  imbedded    in    the    clay  be    examined,  they  are 


CHICAGO  AND  ITS  ENVIRONS. 


found  to  be  partly 
angular  and  partly 
rounded,  but  largely 
sub-angular  with  num- 
erous flat  surfaces  or 
facets  (Fig.  5).  They 
show  neither  the 
rounding  of  shore 
pebbles  nor  the  an- 
gularity of  freshly 
broken  rock.  The 
facets  often  show 
polishing,  parallel  grooving  and 
scratching,  as  though  smoothed  and 
striated  while  being  held  in  a  firm 
position  and  moved  over  a  hard 
surface  beneath. 

The  fine   material  of    the  un- 
stratified    drift,    that    is,   the   blue 
clay  (which  is  sometimes  yellowish 
at  the  surface),  is  found  on  exam- 
ination to  be  made  up  of   minute 
particles  of    rock.      It    is,    in  fact, 
nothing  more   than  finely  pulver- 
ized   rock.      Particles    from    many 
sorts  of  rock  enter  into  its  compo- 
sition,   though    some 
are    abundant    and 
some    rare.      About 
Chicago,   particles   of 
limestone   are    by   far 
the    most     abundant. 
Their     presence     in 
abundance     is    easily 
shown    by  putting    a 
few    drops  of    hydro- 
chloric   acid     on    the 
blue    clay.       It    will, 
as  a    rule,    effervesce 


14  THE  GEOGRAPHY  OF 

briskly.  The  effervescence  is  the  result  of  the  decomposition  of 
the  lime  carbonate  by  the  acid,  the  carbonic  acid  gas  of  the  former 
escaping,  and  causing  the  bubbles. 

The  surface  portion  of  the  clayey  drift  to  the  depth  of  two 
or  three  feet,  is  often  buflfish  or  yellowish  in  color.  This  portion 
does  not  usually  effervesce  when  acid  is  applied,  showing  that  it 
does  not  contain  much  lime  carbonate.  The  reason  of  the  buff, 
non-calcareous  surface  portion,  will  appear  later. 

As  will  be  seen  from  the  list  of  localities  enumerated  above, 
the  unstratified  drift  occurs  sometimes  on  the  low,  flat  plain,  and 
sometimes  on  the  high,  rolling  land  which  borders  it.  In  many 
places  it  is  known  to  run  down  far  below  the  level  of  the  lake, 
lying  on  the  rock  with  no  stratified  drift  beneath. 

In  someplaces  about  the  city,  and  at  numerous  points  through- 
out the  drift-covered  area,  bits  of  timber,  and  even  large  logs  are 
found  in  the  drift.  Vegetable  mould  and  beds  of  peat,  which 
represent  buried  swamps,  are  also  found  both  about  Chicago,  and 
throughout  the  broader  area  of  which  this  forms  a  part.  These 
logs,  beds  of  peat,  etc.,  record  the  fact  that  as  the  glacier  ice 
advanced  over  the  region  it  found  forests,  soils  and  swamps. 
Trees  from  the  forests  were  buried  where  they  grew,  or  more 
commonly  detached  and  carried  forward  by  the  ice  and  incor- 
porated with  its  stony  and  earthy  debris.  The  soils  and  the  peat 
of  the  swamps  sometimes  suffered  a  similar  fate,  but  since  they 
offered  no  resistance  to  the  ice,  they  were  overridden  and  buried 
without  being  carried  forward,  more  commonly  than  trees.  It  is 
manifest  that  if  the  species  of  the  plants  could^be  determined, 
they  would  give  some  clue  as  to  the  climate  preceding  the  advent 
of  the  ice. 

Stratified  drift.  —  In  many  parts  of  the  City  of  Chicago, 
and  at  many  points  outside  the  city  on  the  Chicago  plain,  the 
shallow  excavations  which  are  frequently  to  be  seen  show  the 
upper  part  of  the  drift  to  be  stratified,  and  to  consist  of  sand  and 
gravel,  instead  of  clay  and  stones.  If  the  excavations  be  deep,  the 
blue  clay  with  its  content  of  stones  is  often  exposed  beneath  the 
sand  and  gravel.  The  stones  of  the  stratified  drift  are  usually 
rounded,  and  almost  never  striated.  This  superficial  mantle  of 
stratified  drift  is  wanting  in  many  parts  of  the  plain.  The  strati- 
fied  drift   is,  however,  not   strictly  confined   to  the   plain.      At  the 


CHICAGO  AND  ITS  ENVIRONS.  15 

south  end  of  the  Blue  Island  ridge,  for  example,  there  is  a  consid- 
erable body  of  stratified  drift  running  well  up  to  the  summit  of  the 


Unsubmergeo  Till  Areas. 
II     Till  Area    of  the  Chicago  Pi 
\ ■'■■  ■  \      Sand  and  Gravel  Deposits    o 
Lake  Chicago. 


Fig.  6.     Map  showing  the  general  distribution  of  stratified  sand  and  gravel  and  unstratified 
drift  till  on  the  Chicago  plain. 


i6  THE  GEOGRAPHY  OF 

elevation.  Nor  is  the  stratified  drift  all  at  the  surface,  though  this 
is  where  it  is  most  commonly  seen.  Deep  excavations  sometimes 
show  thin  beds  of  stratified  drift  below  thick  or  thin  bodies  of 
unstratified.  A  complete  explanation  of  the  drift  must  of  course 
take  account  not  only  of  the  unstratified  drift,  but  of  the  stratified 
drift  in  all  its  positions  and  lelations. 

The  general  distribution  of  stratified  drift  on  the  surface  of  the 
plain  is  shown  in  Fig.  6. 

Surface  of  the  rock  bencatJi  the  drift. — These  various  charac- 
teristics of  the  drift,  stratified  and  unstratified,  are  hardly  less  sig- 
nificant, in  the  explanation  of  the  phenomena  about  Chicago,  than 
the  surface  of  the  limestone  beneath.  In  general  it  may  be  said 
that  the  surface  of  the  limestone  where  it  is  accessible  is  relatively 


Fig.  7.    Diagrammatic  section,  showing  the  relation  of  drift  to  bed-rock. 

smooth.  This  statement  is  not  to  be  confused  with  tlie  idea  already 
distinctly  stated,  that  the  surface  of  the  limestone  is  very  uneven. 
What  is  here  meant  is  that  the  surface  of  the  limestone  over  an 
elevation  or  in  a  depression  is,  for  any  small  area,  essentially 
smooth  (Fig.  7).  When  the  limestone  is  uncovered,  its  surface 
frequently  looks  as  if  it   had   just   been   smoothed  or  polished.      It 


i^a-iiiiS 


Diagrammatic  section,  showing  the  relation  of  residuar\ 
lies,  and  from  which  it  has  arisen  hy  de 


iirths  to  tlie  rock  on  which  i 


has  not  the  numerous  little  irregularities  which  characterize  the 
surface  of  limestone  which  has  decayed  under  the  influence  of 
atmospheric  changes  (Fig.  8).  In  such  cases  the  surface  of  the 
limestone  is  irregularly  etched,  and  often  so  soft  and  crumbling 
that  an  exact  line  marking  the  distinction  between  the  earthy  mat- 
ter above  and  the  rock  below  cannot   be   drawn;  but  here  beneath 


CHICAGO  AND  ITS  ENVIRONS. 


17 


the  drift,  the  surface  of  the  limestone  is  in  general  hard  as  well 
as  smooth,  and  the  demarkation  between  it  and  the  drift  is  per- 
fectly definite.  Figs.  7  and  8  put  the  two  types  of  rock  surface  in 
contrast. 

Not  only  is  the  surface  of  the  rock  beneath  the  drift  hard  and 
in  general  smooth,  but  it  is  also  marked  by  numerous  lines  and 
grooves  comparable  to  the  lines  and  grooves  on  the  surfaces  of  the 
stones  of  the  drift.  So  striking  is  the  correspondence  between 
these  marks  on  the  bed-rock  and  those  on  the  stones  of  the  drift, 
that  there  can  be  no  doubt  that  they  owe  their  origin  to  a  common 
cause.  Furthermore,  the  striae  which  are  to  be  seen  on  the  surface 
of  the  limestone  beneath  the  drift  are,  in  any  locality,  essentially 
parallel  to  one  another. 


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Fig.  q.    Abandoned  quarry  at  west  end  of  Stony  Island.    The  figure  shows  the  dip  of  the  rock, 
and  the  general  smoothness  of  its  surface.    The  stris  on  the  surface  do  not  show.     (Harms.) 

The  characteristics  which  have  been  mentioned  as  affecting 
the  surface  of  the  limestone,  as  well  as  many  other  phenomena  which 
need  not  be  here  detailed,  indicate  that  the  limestone  was  worn  in 
such  a  way  as  to  smooth  and  striate  its  surface  at  the  time  the  drip 
was  deposited. 

The  arrows  on  the  map,  Plate  II,  show  the  location  of  the 
striae  which  have  been  observed  about  Chicago,  and  their  direction. 
The  best  exhibition   of  striatj  is  on  the  surface  of  the   rock  at   the 


1 8  THE  GEOGRAPHY  OF 

east  side  of  the  abandoned  quarry  near  the  west  end  of  Stony 
Island.  The  stria;  here  affect  the  upturned  edges  of  strata  which 
have  been  planed  down,  as  well  as  polished  and  scratched.  Here 
as  elsewhere,  striye  are  to  be  seen  on  the  surface  of  tlie  rock  only 
where  the  drift  has  been  recently  removed.  Surfaces  of  limestone 
which  have  long  been  exposed  do  not  show  stria-.  At  the  old 
quarry  on  the  south  side  of  Stony  Island,  striae  may  be  seen  on 
vertical  and  even  on  slightly  overhanging  surfaces. 


Fk;.  lo.  01(1  quarry  on  the  south  side  of  Stony  Island.  The  surface  shown  in  the  tiyiure  does 
not  show  the  stria,  though  it  shows  the  general  smoothing  which  characterizes  glaciated 
surfaces.  Near  the  right  hand  side  of  the  Fig.  near  the  bottom,  the  rock  overhangs. 
On  the  overhanging  surface,  grooving  is  seen,  and  stri;c  may  be  seen  in  the  field.  (Harms.) 

Other  easily  accessible  localities  clearly  showing  glacial  stria- 
are  the  following: 

(i)  In  the  vicinity  of  the  intersection  of  Chicago  avenue  and 
Western  avenue;  (2)  at  Robey  and  Nineteenth  streets;  (3)  at  the 
quarry  of  Dolese  &  Shepard  at  Hawthorne  Station;  (4)  at  the 
Lyons  quarries,  south  of  Riverside;  (5)  in  the  bed  of  the  Des 
Plaines  river  at  low  water,  between  Riverside  and   Summit;  (6)  at 


CHICAGO  AND  ITS  ENVIRONS.  19 

the  quarries  at  Summit;  (7)  at  the  quarry  one  mile  west  of  Elm- 
hurst;  (8)  in  the  creek  south  of  the  bridge  at  Thornton. 

Some  other  localities  are  shown  on  the  map,  but  either  the 
striae  are  not  good,  or  they  are  not  now  easily  accessible. 

The  features  of  the  drift  and  of  the  rock  surface  beneath  which 
have  been  mentioned  as  characterizing  the  region  about  Chicago, 
hold,  in  a  general  way,  over  all  the  millions  of  square  miles  of  ter- 
ritory which  the  drift  affects;  and  the  conclusions  which  follow 
are  based,  not  on  the  phenomena  about  Chicago  alone,  but  on  the 
phenomena  of  this  greater  area,  much  of  which  has  been  studied 
with  great  care. 

The  drift  is  of  glacial  origin. — The  characteristics  of  the  un- 
stratified  drift,  together  with  the  characteristics  of  the  surface  of 
the  rock  on  which  it  lies,  point  in  no  uncertain  way  to  the  origin 
of  the  drift  and  its  accompanying  phenomena.  The  drift  is  identi- 
cal in  kind  with  the  deposits  now  being  made  by  glaciers  in  vari- 
ous parts  of  the  world,  and  the  characteristics  of  the  surface  of  the 
rock  beneath  the  drift  are  identical  with  those  of  the  surface  of 
rock  over  which  glacier  ice  is  known  to  have  recently  passed. 
These  points  are  easily  demonstrable.  * 

In  many  regions  existing  glaciers  are  diminishing  in  size,  and 
are  therefore  bordered  by  areas  which  they  recently  occupied,  but 
from  which  the  ice  has  now  melted.  In  such  situations  both  the 
debris  deposited  by  the  ice  (the  drift)  and  the  surface  of  the  rock 
on  which  it  rests,  are  accessible.  Here  the  surface  of  the  rock  is 
found  to  be  smoothed  and  polished,  and  marked  by  lines  or 
grooves  essentiall}'  parallel  to  one  another,  while  on  it  rests  a 
mantle  of  debris  of  variable  thickness,  made  up  of  bowlders  or 
smaller  pieces  of  rock,  imbedded  in  a  clayey  matrix  composed  of 
pulverized  rock,  the  mixture  being  without  stratirication.  The 
stones  are  more  or  less  faceted  and  striated.  With  this  unstrati- 
fied  debris  there  is  often  associated  some  which  is  stratified. 

Furthermore,  the  lower  portion  of  existing  glaciers  may  some- 
times be  seen,  and  the  lower  part  of  the  ice  is  thickly  set  with  a 
quantity  of  earthy,  sandy  and  stony  material  of  all  grades  of  coaise- 
ness  and  fineness.  With  these  materials  imbedded  in  its  lower 
portion,  the  ice  moves  slowly  forward,  resting  down  upon  the  sur- 
face over  which  it  passes  with  the  whole  weight  of  its  mass.  The 
grinding  action   between  the  stony  matter  in  the  bottom  of  the  ice 


20  THE  GEOGRAPHY  OF 

and  the  rock  bed  over  which  it  moves,  is  powerful.  The  coarse 
material  in  the  bottom  of  the  ice  grooves  and  scratches  the  bed 
over  which  it  is  borne,  while  the  fine  material,  like  clay,  polishes 
the  surface  over  which  it  is  moved. 

At  the  same  time  that  the  material  is  carried  forward  in  the 
bottom  of  the  ice  and  used  to  grave  the  surface  of  the  rock  beneath, 
the  stones  in  transit  are  themselves  worn,  for  the  bed-rock  reacts 
on  them.  Like  the  bed-rock,  they  are  striated.  One  surface  of  a 
stone  in  the  ice  is  at  one  time  held  against  the  bed-rock,  and  worn 
flat  and  polished  or  striated.  The  stone  may  then  be  turned,  and 
in  the  new  position  a  new  flat  surface  may  be  developed.  The 
stones  in  the  ice  may  be  worn,  not  only  by  the  bed-rock,  but  by  one 
another.  Thus  they  may  be  striated  on  several  or  all  sides,  and 
because  the  stone  may  change  its  position  from  time  to  time,  the 
striae  may  run  in  any  direction  (Fig.  5).  The  bed-rock,  on  the  other 
hand,  not  being  free  to  move,  is  striated  in  one  direction  only.  Its 
stria,",  therefore,  and  not  those  of  the  stones  of  the  drift,  show  the 
direction  of  ice  movement  after  the  ice  has  melted. 

So  unique  and  so  distinctive  are  the  results  of  the  work  of 
glacier  ice  that  they  cannot  be  mistaken  for  the  work  of  any  other 
agency;  and  so  many  and  so  striking  are  the  points  of  correspond- 
ence between  the  work  of  existing  glaciers  and  the  work  of  the 
agencies  which  produced  the  drift  about  Chicago  (and  the  large 
drift-covered  area  about  it),  that  there  is  no  escape  from  the  con- 
clusion that  the  latter,  with  all  its  accompanying  phenomena,  is  the 
work  of  glacier  ice. 

In  the  valleys  and  on  the  plains  beyond  the  existing  glaciers 
there  are  frequently  deposits  of  stratified  sand  and  gravel,  borne 
out  beyond  the  ice  by  waters  which  came  from  its  melting.  Water 
action  necessarily  accompanies  glacier  action,  and  the  deposits 
made  by  water  are  stratified.  Every  glacier,  therefore,  gives  rise  to 
water,  which  is  sure  to  stratify  more  or  less  of  the  material  which 
the  ice  had  deposited,  or  which  it  was  carrying.  It  is  through  the 
agency  of  water,  therefore,  that  the  stratified  drift  accompanying 
the  unstratified  is  to  be  explained.  It  will  be  seen  in  the  sequel 
that  the  water  which  stratifies  the  drift  may  be  lake  or  sea  water, 
as  well  as  that  of  streams. 


CHICAGO  AND  ITS  ENVIRONS. 


II. 

DEVELOPMENT  OF  THE  PRESENT  GEOGRAPHY. 

The  preceding  pages  should  have  made  it  clear  that  two  for- 
mations determine  the  geography  of  Chicago.  These  are  the  rock, 
and  the  drift  which  overlies  it. 

THE  GEOGRAPHY  OF  THE  ROCK  SURFACE. 

After  the  Niagara  limestone  was  deposited,  and  after  such 
younger  beds  as  once  covered  it  had  been  laid  down  on  it,  the  sea 
retired  from  this  region,  either  because  its  waters  were  drawn  off 
by  the  sinking  of  the  deeper  parts  of  the  ocean  bottom  elsewhere,  or 
because  this  section  of  the  earth's  crust  was  warped  upward  suf- 
ficiently to  bring  it  above  the  level  of  the  sea.  So  soon  *s  it 
became  land,  its  surface  was  exposed  to  the  action  of  heat  and 
cold,  of  rain  and  wind,  of  plants  and  animals.  Of  primary 
importance  was  the  rain,  and  the  streams  to  which  the  rain  gave 
rise.  These  streams,  working  as  streams  have  always  worked, 
began  to  cut  valleys  in  the  surface  of  the  land,  and  ultimately 
wore  away  much  of  the  rock,  carrying  the  eroded  material  back  to 
the  sea.  During  the  long  period  which  followed  the  deposition  of 
the  youngest  marine  beds,  almost  all  of  the  formations  down  to 
the  Niagara  were  carried  away  by  erosion.  Not  only  were  the 
formations  above  the  Niagara  destroyed,  but  the  surface  of  the 
Niagara  limestone  itself  was  deeply  eroded  by  the  same  processes 
which  had  carried  away  the  overlying  beds.  The  cutting  of  val- 
leys in  the  surface  of  the  limestone  left  ridges  and  hills  between 
them,  and  the  surface,  at  the  close  of  the  long  period  of  erosion, 
was  even  rougher  than  that  which  now  affects  the  limestone 
beneath  the  drift. 

In  northwestern  Indiana,  the  Niagara  limestone  is  overlain 
by  Devonian  formations.  At  the  junction  of  the  Des  Plaines  and 
Kankakee  rivers  is  found  the  northeast  margin  of  the  formations 
of   the   Carboniferous   system    (next  younger   than  the  Devonian), 


22  THE  GEOGRAI'HY  OF 

which  covers  most  of  tlie  State,  while  farther  west,  in  Iowa  and 
beyond,  the  systems  of  the  Mesozoic  and  early  Cenozoic  eras 
overlie  the  Carboniferous.  The  mantle  of  drift  which  covers  the 
Niagara  limestone  of  Chicago,  covers  all  these  systems  of  strata. 
It  is  therefore  evident  that  all  the  vast  geologic  periods  represented 
by  these  several  systems  of  rock  must  have  intervened  between  the 
deposition  of  the  Niagara  limestone,  and  that  of  the  mantle  of 
bowlder  clay  which  rests  on  its  surface.  These  relations  show 
that  the  period  of  erosion  following  the  deposition  of  the 
Devonian  beds  and  preceding  the  deposition  of  the  drift,  was 
very  long.' 

THE  GLACIAL  PERIOD. 

The  long  period  during  which  the  rock  beds  of  this  region 
were  exposed  to  the  ordinary  agencies  of  rock  disintegration  and 
erosion  was  brought  to  a  close  by  climatic  changes  the  like  of 
which  had  never  occurred  in  this  latitude,  so  far  as  now  known,  in 
all  the  earth's  history.  This  change  consisted  in  the  development 
of  arctic  conditions,  not  only  about  Chicago,  but  over  a  wide  area 
in  the  northern  and  northeastern  parts  of  the  United  States,  as 
well  as  over  a  still  larger  area  farther  north.  Under  the  influence 
of  these  conditions,  a  vast  continental  ice-sheet,  comparable  to 
that  which  now  covers  Greenland,  though  many  times  larger,  came 
into  existence.  Its  area,  when  at  its  maximum,  is  represented  in 
Fig.  u.  The  cause  of  the  climatic  change  which  brought  about 
the  glacial  conditions  it  not  here  discussed.  Conjecture  has 
attributed  it  now  to  great  changes  in  the  orbit  or  axis  of  the  earth, 
now  to  changes  in  the  elevation  or  distribution  of  the  land,  and 
now  to  changes  in  the  constitution  of  the  atmosphere,  as  well  as 
to  many  other  changes,  real  or  speculative.  Sufifice  it  to  say,  that 
scientists  are  by  no  means  agreed  as  to  the  hypothesis  which  best 
explains  the  facts.  Whatever  the  cause,  the  fact  that  a  great  ice- 
sheet,  about  4,000,000  square  miles  in  area,  came  into  existence  in 
the  northern  part  of  the  continent,  is  no  longer  open  to  ques- 
tion.     As  already  pointed  out,  the  proof  is  found  in  the  character 

'Tliis  period  of  erosion  is  here  spoken  of  as  if  it  wore  continuous,  tfiouRh  tliis  may  not 
have  been  the  case;  but  for  our  present  purpose,  it  is  not  important  to  recite  the  many  eleva- 
tions and  depressions,  and  perhaps  the  submergences  and  emergences  which  this  region  is 
icnown  to  or  thoufjht  to  have  suffered  since  tlie  deposition  of  the  Devonian  beds. 


CHICAGO  AND  ITS  ENVIRONS. 


23 


of  the  drift,    and  in  the   peculiar  and   distinctive  features  of   the 
rock  surface  beneath  it. 


Fil;  11  Sliows  the  area  covertd  by  ice  during  that  epoch  of  the  Glacial  Period  when  the  ice 
was  most  extensively  developed.  The  main  centers  of  accumulation  are  also  shown. 
There  were  many  small  centers  of  glaciation  in  the  mountains  south  of  the  main  ice- 
sheet.    (After  Ch'ambcrlin.i 

The  results  of  careful  and  extensive  study  of  the  drift  in 
North  America  have  led  those  geologists  who  have  concerned 
themselves  especially  with  the  drift,  to   the   confident   conclusion 


24  THE  GEOGRAPHY  OF 

tliat  the  glacial  period  consisted  of  several  more  or  less  distinct 
glacial  epochs,  separated  b\'  epochs  which  have  been  called  inter- 
glacial.  During  the  glacial  epochs,  the  climate  was  severe,  and 
the  ice-sheets  were  being  enlarged  ;  during  the  interglacial  epochs 
the  climate  was  less  severe,  and  the  ice-sheets  diminished  in  area  and 
thickness,  if  indeed  they  did  not  altogether  disappear.  During 
these  mild  intervals,  plants  and  animals  returned  to  latitudes 
from  which  they  had  been  driven  by  the  cold  and  ice,  only  to  be 
driven  southward  again  with  the  advent  of  the  next  epoch  of 
rigorous  climate. 

The  most  extensive  invasion  of  the  ice  reached  the  Ohio 
river  in  Ohio  and  Indiana,  and  farther  west  reached  northeast- 
ern Kansas.  West  of  that  point  the  margin  of  the  ice  was  not 
far  from  the  Missouri  river. 

The  ice-sheets  of  several  of  the  glacial  epochs  passed  over 
northeastern  Illinois,  and  each  contributed  to  the  aggregate 
effects  of  glaciation.  In  the  paragraphs  which  follow,  it  is  the 
effects  of  glaciation,  rather  than  the  effects  of  the  ice  of  any  one 
glacial  epoch,  which  are  referred  to;  yet  the  effects  of  the  last 
glacial  epoch  on  the  geography  of  Chicago  are  of  so  much  more 
importance  than  those  of  the  others,  that  the  chief  emphasis  is 
laid  on  its  results.  It  should  be  noted,  however,  that  some  of 
the  great  geographic  features  of  the  region,  such  as  the  basin  of 
Lake  Michigan,  may  have  been  formed  before  the  latest  advance 
of  the  ice  and,  perhaps,  much  before.' 

Development  of  the  ice-sheet. — The  especial  feature  of  the  gla- 
cial period  was  an  ice-sheet  of  continental  dimensions.  The 
climate  which  preceded  and  caused  the  development  of  this  ice- 
sheet,  probably  came  on  gradually,  and  the  growth  of  the  ice-sheet 
was  probably  slow.  To  gain  a  conception  of  the  origin  of  the 
ice-sheet  a  few  familiar  principles  may  be  recalled. 

The  temperature  and  the  snowfall  of  a  region  may  stand  in 
such  a  relationship  to  each  other,  that  the  summer's  heat  may 
barely  suffice  to  melt  the  winter's  snow.  If  under  these  circum- 
stances the  annual  temperature  were  to  be  reduced,  or  the  fall  of 
snow  increased,  the  summer's  heat  would  fail  to  melt  the  winter's 
snow,   and  some  portion  of  the  snow   would  endure   through  the 

'A  summary  of  opinions  as  to  the  time  and  mode  of  origin  of  tiu' Great  Lake  basins  is 
given  l>y  Alexander  Winchell  in  the  American  Geologist,  Vol.  XIX,  1897. 


CHICAGO  AND  ITS  ENVIRONS.  25 

summer.  Were  this  condition  once  inaugurated,  the  depth  of  the 
snow  would  increase  from  year  to  year,  and  at  the  same  time  the 
area  of  the  snow-field  would  be  enlarged,  since  the  presence  of 
the  snow  would  so  far  reduce  the  temperature  of  the  surround- 
ing territory  as  to  increase  the  proportion  of  the  precipitation 
which  would  there  fall  as  snow.  In  the  course  of  time,  and  under 
favorable  conditions,  the  area  of  the  snow-field  and  the  depth  of 
the  snow  would  become  great.  If  at  the  same  time  the  climatic 
changes  which  occasioned  the  snow-field  continued  to  act  with 
increasing  effect,  the  total  result  would  be  still  greater. 

As  in  the  case  of  snow-fields  to-day,  the  greater  part  of  the 
snow-mass  would  eventually  be  converted  into  ice.  Several  fac- 
tors would  be  effective  in  accomplishing  this  result.  The  pres- 
sure of  the  overlying  snow  would  tend  to  compact  the  lower 
portions  of  the  snow  into  ice,  and  water  arising  from  the  melting 
of  the  surface  snow  by  the  sun's  heat  and  percolating  through  the 
superficial  layers  of  the  snow,  might  freeze  below,  taking  the  form 
of  ice.  By  these  and  other  changes  the  snow-field  becomes  an 
ice-field,  the  snow  being  restricted  to  its  superficial  parts.  • 

Eventually  the  increase  in  the  depth  of  the  snow  will  give 
rise  to  other  phenomena.  When  the  thickness  of  the  ice  has 
become  considerable,  the  pressure  upon  its  lower  parts  will  be 
great.  We  are  wont  to  think  of  ice  as  a  brittle  solid.  If  in  its 
place  we  had  some  slightly  plastic  body,  which  would  yield  to 
pressure,  it  is  evident  that  the  weight  of  the  overlying  portions 
would  press  out  the  lower  parts  of  the  mass,  and  that  these  would 
spread  in  all  directions  by  a  sort  of  iiowing  motion. 

Under  great  pressure  many  substances  which  otherwise  appear 
to  be  solid  exhibit  the  characteristics  of  plastic  bodies.  Among 
the  substances  exhibiting  this  property,  ice  is,  perhaps,  best 
known.  Brittle  and  resistant  as  it  seems,  it  may  be  moulded  into 
almost  any  desired  form  if  subjected  to  sufficient  pressure,  steadily 
applied  through  long  intervals  of  time.  The  changes  of  form 
which  may  thus  be  produced  in  ice  are  brought  about  without 
visible  fracture  in  its  mass.  Concerning  the  exact  nature  of  the 
movement  which  takes  place  between  the  particles,  there  may  be 
some  question,  but  the  result  appears  to  be  such  as  would  be 
brought  about  if  the  ice  were  capable  of  flowing,  with  extreme 
slowness,  under  great  pressure  continuously  applied. 


26  THE  GEOGRAPHY  OF 

In  the  ice-field  supposed,  we  have  the  conditions  for  f,'reat 
pressure  and  for  its  continuous  application.  If  the  ice  be  caj>a- 
ble  of  motion  as  a  plastic  body,  the  result  would  be  that  the 
great  weight  of  ice,  pressing  down  upon  the  lower  parts  of  the 
ice  field,  would  induce  a  gradual  movement  of  the  ice  outward 
from  the  deepest  part  of  the  field,  so  that  areas  surrounding  the 
region  of  snow  accumulation,  would  gradually  be  encroached  upon 
by  the  ice.  Observation  shows  that  this  is  what  takes  place  in 
every  snow-field  of  sufficiently  great  extent  and  depth.  Motion 
thus  brought  about  is  glacier  motion,  and  ice  thus  moving  is 
glacier  ice. 

Greenland  affords  an  example  of  the  conditions  here  described. 
A  large  part  of  the  half  million  square  miles  which  this  body  of 
land  is  estimated  to  contain,  is  covered  by  a  vast  sheet  of  snow 
and  ice,  hundreds  and  thousands  of  feet  in  thickness.  In  this 
field  of  ice  and  snow  there  is  continuous,  though  very  slow  move- 
ment. The  ice  creeps  slowly  out  from  the  heart  of  the  icy 
continent  by  a  sort  of  flowing  motion,  and  advances  to  the  south 
and  east  and  north  and  west  until  it  reaches  territory  where  the 
climate  is  such  as  to  waste  (melt  and  evaporate)  the  ice  as  rapidly 
as  it  advances. 

The  edge  of  the  ice  does  not  remain  fixed  in  position.  There 
is  reason  to  believe  that  it  alternately  advances  and  retreats, 
according  as  the  ratio  between  movement  and  waste  increases  or 
decreases.  These  oscillations  in  position  are  doubtless  connected 
with  climatic  changes. 

The  ice-sheets  of  northeastern  North  America  appear  to  have 
had  more  than  one  center  of  growth.  One  main  center  lay  east  of 
Hudson  Bay,  and  another  west  of  it  (Fig.  1 1).  There  were  perhaps 
other  minor  centers,  but  ultimately  the  snow-fields,  extending 
themselves  from  their  several  centers,  united,  and  the  resulting 
ice-sheet  is  commonly  spoken  of  as  a  unit. 

In  addition  to  the  ice-cap  of  the  northeastern  part  of  the 
continent,  there  was  an  ice-sheet  in  the  northwestern  part.  This 
extended  eastward  from  the  mountains  and  joined  the  one  origi- 
nating farther  east,  near  our  national  boundary,  in  the  longitude  of 
Montana. 

The  centers  of  ice  accumulation  are,  on  the  whole,  higher 
than  their  surroundings,  so   that  if  the   relative  elevations   of  the 


CHICAGO  AND  ITS  ENVIRONS.  27 

different  parts  of  the  continent  were  the  same  as  now,  the  ice 
moved  from  higher  to  lower  lands.  The  surface  of  the  land  is, 
however,  so  uneven,  and  its  inclination  so  slight,  that  some 
cause  of  movement  other  than  its  inclination  must  be  involved. 
Furthermore,  since  the  ice  passed  over  valleys,  hills,  and  even 
mountains,  without  having  its  general  direction  of  movement 
notably  affected  by  them,  it  is  clear  that  its  motion  was  not  con- 
trolled primarily  by  the  slope  of  the  surface  on  which  it  rested. 

The  direction  of  flow'  of  any  liquid  substance  depends,  not 
immediately  on  the  slope  of  its  bed,  but  on  the  slope  of  its  upper 
surface.  For  the  surface  of  the  ice  to  have  had  sufficient  slope  to 
cause  the  movement,  its  thickness  must  have  been  great.  The 
limit  of  the  ice  in  southern  Illinois  is  something  like  1,000  miles 
from  the  center  of  the  ice-sheet.  How  much  slope  of  the  upper 
surface  would  suffice  to  cause  the  movement  which  actually  took 
place? 

Various  estimates  of  the  slope  of  the  surface  of  the  ice  have 
been  made.  If  the  slope  were  no  more  than  10  feet  per  mile,  and 
this  seems  like  a  very  moderate  estimate,  the  thickness  of^the 
ice  would  have  been  10,000  feet  at  the  center  of  accumulation,  if 
this  slope  held  fro7n  margin  to  center.  It  is  possible  that  even  this 
low  angle  of  slope  is  excessive  as  an  average.  Near  the  margin  of 
the  ice-sheet,  and  this  is  the  only  place  where  its  former  surface 
slope  can  now  be  determined,  the  slope  was  certainly  much 
greater  than  this,  but  with  increasing  distance  from  the  margin  the 
slope  became  less  and  less. 

Whatever  the  slope,  the  ice  in  the  northeastern  part  of  the 
continent  was  thick  enough,  except  at  its  very  margin,  to  fill  all 
valleys  and  basins,  and  to  cover  all  hills  and  ridges  within  its  area, 
and  some  of  the  mountains  covered  rise  3,000  or  4,000  feet  above 
their  surroundings. 

When  the  ice  covered  the  region  about  Chicago,  its  surface 
was  probably  essentially  smooth,  and  not  notably  affected  by  the 
topography  of  the  rock  beneath.  Its  surface  must  have  been 
many  hundred  feet  above  the  surface  of  the  highest  rock  hills  of 
the  region.  Though  the  irregularities  of  the  rock  surface  probably 
caused  deflections  of  movement  in  the  lower  part  of  the  ice,  its 

'It  15  not  meant  to  assert  that  the  ice  actually  flows.  This  is  open  to  question;  but  the 
result  of  its  movement  is  very  much  the  same  as  it  would  be  if  it  actually  flowed. 


28 


THE  GEOGRAPHY  OF 


movement  as  a  whole  seems  not  to  have  been  much  affected  by 
any  topographic  feature  immediately  about  Chicago,  unless  by 
the  lake  basin  itself. 

The  erosion  ivork  of  the  ice. — When  the  ice  invaded  this  region, 
the  surface  was  probably  covered  with  a  mantle  of  soil  and  decayed 
rock,  and  vegetation  was  probably  growing  upon  it.  In  its  move- 
ment, the  ice  soon  incorporated  in  its  lower  part  much  of  the  veg- 
etation, soil  and  decayed  rock.  So  soon  as  these  loose  materials 
were  removed,  the  surface  of  the  rock  beneath  was  exposed  to  wear, 
and  the  advancing  ice  polished,  scratched  and  grooved  it  by  means 
of  the  earthy  matter  and  rock  fragments  which  it  slowly  but  steadily 
carried  forward.  The  rock  fragments  in  the  ice  were  themselves 
ground,  striated  and  polished  at  the  same  time,  and  perhaps 
crowded  farther  up  into  the  ice  and  borne  onward  with  the  load  of 
debris. 


Fu;.  13.    Diagrammaiic  riguru,  showing  the  effect  of  ice  wear  on  a  hill  of  rock,  such  as  tliat 
shown  in  Fig.  12,  after  it  has  been  overridden  l)y  the  ice. 

The  wear  effected  by  the  rock-shod  ice  was  not  confined  to  a 
mere  marking  of  the  surface  over  which  it  passed.  Where  promi- 
nences of  rock  obstructed  its  progress,  they  were  acted  upon  with 
a  force  proportional  to  their  great  resistance,  and  suffered  a  corre- 
sponding measure  of  abrasion.  They  were  worn  most  on  the  sides 
which  faced  the  movement — that  is,  on  their  stoss  sides.  All 
roughnesses  of  surface  and  all  projecting  angles  of  rock,  being 
pressed  upon  with  especial  force,  would  in  the  course  of  time  be 
reduced  if  not  obliterated.  Such  as  escaped  destruction  would 
come  to  have  not  merely  polished  and  striated  surfaces,  but 
rounded  forms,  with  the  greatest  wear  and  gentlest  slopes  on  their 


CHICAGO  AND  ITS  ENVIRONS.  29 

stoss  sides  (Fig.  13).  Even  the  minor  rugosities  of  a  glacier's  bed 
will  suffer  wear  in  a  similar  manner,  and,  until  entirely  effaced,  will 
present  similar  forms. 

The  erosive  effect  of  the  ice  was  therefore  to  grind  down  the 
elevations  and  to  make  rough  surfaces  smooth.  The  rock  surface 
beneath  Chicago  and  its  environs  still  remains  about  as  it  was  left 
by  the  ice.  Could  it  be  seen,  it  would  be  found  to  be  wanting  in 
the  many  little  rugosities  which  affect  surfaces  eroded  subaerially. 

At  the  same  time  that  the  hills  of  rock  were  worn  down  by  the 
ice,  depressions  in  the  rock  were  in  some  cases  made  deeper.  This 
is  especially  true  where  the  ice  moved  through  a  valley  lengthwise. 
Where  it  crossed  a  valley,  its  effect  was  to  wear  down  its  borders, 
rather  than  its  bottom. 

The  moving  ice  must  have  covered  the  site  of  Chicago  for  long 
periods  of  time.  During  that  glacial  epoch  when  the  advance  of 
the  ice  was  greatest,  its  stay  in  this  region  began  when,  coming 
down  from  the  north,  it  reached  this  latitude.  Glacier  ice  remained 
over  this  locality  while  the  edge  of  the  ice  was  advancing  some  150 
miles  farther  south,  during  such  time  as  the  edge  remained  sta- 
tionary in  this  advanced  position,  and  during  the  time  occupied  in 
melting  its  edge  back  again  to  this  region.  If  the  edge  of  the 
ice  advanced  and  retreated  at  the  rate  of  but  a  few  feet  per  day, 
it  will  be  seen  that  a  very  long  period  of  time,  several  thousands 
of  years  at  least,  would  be  needed.  During  other  ice  epochs, 
when  the  ice  advanced  less  far  to  the  south,  its  stay  may  not  have 
been  so  long. 

Deposits  made  by  the  ice. — On  melting,  glacier  ice  leaves  its 
former  bed  covered  with  the  debris  which  it  carried,  chiefly  in  its 
lower  part.  Were  this  material  equally  distributed  in  the  ice  dur- 
ing its  motion,  and  were  the  conditions  of  its  deposition  every- 
where the  same,  the  drift  would  constitute  a  mantle  of  uniform 
thickness  over  the  underlying  rock.  Such  a  mantle  of  drift  would 
not  greatly  alter  the  topography.  It  would  simply  raise  the  sur- 
face by  an  amount  equal  to  the  thickness  of  the  drift,  leaving 
elevations  and  depressions  of  the  same  magnitude  as  before,  and 
sustaining  the  same  relations  to  one  another.  But  the  drift  carried 
by  the  ice,  in  whatever  position,  was  not  equally  distributed  dur- 
ing the  process  of  transportation,  and  the  conditions  under  which 
it  was  deposited  were  not  constant  in  the  same  area,  much  less  in 


30 


THE  GEOGRArilV  OF 


different  ones.  Because  of  tfie  unequal  amounts  of  material  carried 
by  different  parts  of  the  ice,  and  because  of  the  unequal  and  incon- 
stant conditions  of  deposition  under  the  body  of  the  ice  and  its 
edge,  the  mantle  of  drift  has  a  very  variable  thickness;  and  a 
mantle  of  drift  of  variable  thickness  cannot  fail  to  modify  the  topog- 
raphy of  the  region  it  covers  (see  Fig.  2).  The  extent  of  the 
modification  will  depend  on  the  extent  of  the  variation  in  thick- 
ness. This  amounts,  in  our  region,  to  150  feet  or  more,  and  on 
our  continent  to  upwards  of  500  feet.  The  continental  ice-sheet 
therefore  modified  the  topography  of  the  region  it  covered,  not 
only  by  the  wear  it  effected,  but  also  by  the  deposits  it  made. 

About  Chicago  the  average  thickness  of  the  drift  on  the  high- 
lands is  greater  than  on  the  low.  From  this  it  might  be  inferred 
that  the  relief  of  the  present  surface  about  Chicago  is  greater  than 
it  would  have  been  without  the  drift.  But  this  is  probably  not 
the  fact,  for  there  are  somewhat  deep  valleys  in  the  surface  of  the 
rock  beneath  the  Chicago  plain,  and  they  increase  the  relief  of  the 
rock  surface  notably.  At  any  rate, the  angles  of  slopes  of  the  pres- 
ent surface  are  probably  notably  less  than  some  of  the  angles  of 
slope  of  the  rock  surface  beneath  the  drift.  Reference  has  already 
been  made  to  the  belt  of  thick  drift  which  skirts  the  Chicago 
plain.  The  greater  thickness  of  drift  along  this  belt  seems  to 
have  resulted  from  the  halting  of  the  ice  edge  in  this  position, 
during  its  final  retreat.  If  the  edge  of  the  ice  had  melted  back  at 
a  constant  rate,  its  position  at  one  stage  would  not  be  marked  by 
notably  more  drift  than  its  position  at  another  ;  but  if  its  edge 
remained  in  a  given  position  for  a  time,  drift  was  being  continually 
brought  to  that  position  by  the  forward  motion  of  the  ice,  and  not 
carried  beyond.  Under  the  stationary  edge,  therefore,  a  belt  of 
drift,  thicker  than  that  on  either  side,  might  be  accumulated. 
This  is  the  explanation  of  the  Valparaiso  moraine  (PI.  II)  and  of 
submarginal  moraines  in  general.  In  its  greater  thickness  only 
does  it  differ  from  the  ground  moraine  which  the  great  body  of  the 
drift  constitutes. 

Not  only  did  the  deposition  of  the  drift  affect  the  topography 
about  the  city  by  diminishing  (probably)  the  relief  and  by  obliter- 
ating the  more  striking  depressions  in  the  surface  of  the  rock,  but 
its  surface  had  a  topography  of  its  own.  Like  glacial  deposits  in 
general,    its   surface,    as   left    by  the    ice,    was   undulatory,    being 


CHICAGO  AND  ITS  ENVIRONS.  -  31 

marked  by  many  minor  and  gentle  elevations  and  depressions,  the 
latter  often  without  outlets.  In  our  own  region  this  rolling  topog- 
raphy, marked  by  low  swells  and  basin-like  or  saucer-like  depres- 
sions, is  common  outside  the  Chicago  plain.  The  same  topography 
is  wide-spread  throughout  the  whole  area  affected  by  drift.  In  the 
depressions  lie  many  of  the  ponds  and  lakes  which  abound  in  the 
glaciated  part  of  our  country. 

The  topography  of  the  region  as  left  by  the  ice  was  then  the 
result  of  the  superposition  of  an  unequally  thick  mantle  of  drift,on 
an  uneven  surface  of  rock. 


LAKE  CHICAGO. 

Origin. — Every  ice-sheet  has  a  period  of  advance  followed  by 
a  period  of  decline.  In  the  former,  the  growth  of  the  ice-field 
exceeds  its  waste,  and  in  the  latter  the  waste  exceeds  the  growth. 
The  duration  of  the  last  ice-sheet  in  the  region  is  unknown,  but  it 
is  probably  to  be  reckoned  in  thousands  of  years.  When  the  con- 
ditions became  such  that  the  ice  front  was  melted  back  faster  than 
it  advanced,  the  final  retreat  of  the  ice  began.  While  the  edge  of 
the  ice  was  being  melted  back  to  the  Valparaiso  moraine,  and  while 
it  stood  in  that  position,  the  water  which  arose  from  its  melting 
flowed  off  to  the  south.  That  from  Northern  Illinois  found,  its 
way  by  various  valleys  to  the  Mississippi,  and  thence  to  the  sea. 
One  line  of  drainage  was  down  the  Des  Plaines  valley  to  the  Illi- 
nois. When  the  ice  retreated  northeast  of  the  Valparaiso  moraine, 
the  depression  between  the  ice  front  on  the  one  side,  and  the 
moraine  ridge  on  the  other,  was  flooded  with  glacial  water,  and  a 
lake,  marginal  to  the  ice,  came  into  existence.  As  the  edge  of  the 
ice  which  formed  one  shore  of  the  lake  retreated  northward,  the 
lake  enlarged.  Its  water  rose  until  it  reached  a  level  about  60 
feet  above  the  present  surface  of  Lake  Michigan,  when  it  over- 
flowed to  the  west  along  the  line  of  the  present  Des  Plaines  river 
valley  and  through  the  Sag  (see  Fig.  14,  also  Frontispiece  and 
PI.  II,  page  8). 

The  accumulation  of  water  between  the  moraine  and  the  ice 
was  the  beginning  of  what  has  been  called  Lake   Chicago,^  in  some 

'  Leverett.— The  Pleistocene  Features  and  Deposits  of  the  Chicago  Area.  Bull.  II.. 
Geol.  and  Nat.  Hist.  Surv.,  Chicago  Academy  of  Sciences,  p.  57,  iSgy. 


32  THE  GEOGKA/'HY  OF 

sense  the  ancestor  of  the  present  Lake  Michigan.  This  lake  is 
the  third  great  factor  to  be  considered  in  studying  the  geography 
of  this  region.  The  lines  of  drainage  which  developed  into  the 
present  Des  Plaines  valley  and  the  Sag  tributary  to  it,  have  long 
been  known  as  the  Chicago  outlet. 

The  Chicago  outlet. — The  general  features  of.  the  outlet  have 
already  been  given.  Near  Lemont,  the  valley  is  largely  cut  in 
rock,  the  limestone  beds  rising  40  to  60  feet  above  the  valley  bot- 
tom on  either  side.  This  valley  is  probably  not  preglacial,  though 
it  may  have  antedated  the  last  glacial  epoch.  If  so,  it  was  largely 
filled  with  drift  during  that  epoch.  The  top  of  the  rock  in  the 
bluffs  has  about  the  same  elevation  as  that  of  the  waters  of  Lake 
Chicago  at  its  highest  stage. 

At  its  maximum,  the  discharge  of  water  through  this  outlet 
must  have  been  comparable  to  that  now  discharged  through  the 
Niagara  river.  Below  Lemont,  the  bed  of  the  outlet  declines  90 
feet  in  25  miles.  Of  this  fall  76  feet  is  made  in  less  than  10  miles, 
between  Romeo  and  the  Joliet  pool.  The  nature  of  the  rock  is 
such  that  it  is  not  probable  that  a  waterfall  was  established,  but 
the  high  gradient  must  have  caused  strong  rapids. 

Stages. — There  were  several  more  or  less  distinct  stages  in 
the  history  of  Lake  Chicago.  During  the  first  stage,  which  has 
been  recognized  (the  Glenwood  stage),  its  water  seems  to  have 
stood  about  60  feet  above  the  level  of  Lake  Michigan.  This  stage 
lasted  for  a  considerable  period  of  time,  during  which  the  waves 
and  currents  did  their  appropriate  work.  Where  they  cut  into 
the  shores  they  developed  cliffs;  where  they  were  depositing 
instead  of  eroding,  they  made  beaches  and  spits  of  sand  and 
gravel.  All  this  time  the  ice  may  have  been  melting  back,  so 
that  the  ice-shore  of  the  lake  was  receding  to  the  northeastward, 
and  the  area  of  the  lake  increasing. 

Following  this  maximum  stand  of  Lake  Chicago,  when  its 
waters  were  60  feet  higher  than  those  of  Lake  Michigan,  there 
was  a  stage  during  which  the  waters  are  thought  to  have  been  too 
low  to  discharge  through  the  outlet  to  the  west,  or  even  to  cover 
all  of  the  Chicago  plain.  On  this  plain,  so  far  as  not  covered 
with  water,  vegetation  gained  a  foothold,  and  where  marshy  con- 
ditions prevailed,  distinct  deposits  of  peat  were  formed.  This  was 
the  second  stage  of   the    lake.      The    reason  for   the  lowering  of 


CHICAGO  AND  ITS  ENVIRONS.  33 

the  lake  level  at  this  stage  is  not  known.  Probably  the  ice  had 
retreated  so  far  to  the  north  as  to  open  an  outlet  in  that  direc- 
tion, lower  than  that  via  the  Des  Plaines  and  Illinois. 

Later,  the  water  of  the  lake  rose  again,  though  not  so  high 
as  before,  covering  the  plain  and  burying  the  peat  and  other 
vegetal  deposits  under  accumulations  of  sand  and  gravel.  This 
rise  of  the  lake  was  the  beginning  of  its  third  stage  (the  Calumet 
stage).  The  cause  of  the  rise  of  the  water  may  have  been  an 
advance  of  the  ice  from  the  north,  blocking  the  outlet  of  the  pre- 
ceding stage,  or  a  rise  of  the  land  to  the  north,  raising  the  outlet 
in  that  direction,  and  with  it  the  level  of  the  lake.  As.  the  waters 
rose  the  discharge  through  the  southwestern  outl™  was  again 
resumed.  The  third  stage  of  the  lake  has  left  a  record  in  a  sec- 
ond line  of  beaches  about  40  feet  above  the  level  of  Lake  Michi- 
gan, and  about  20  feet  below  that  of  the  first  recorded  stage. 

The  outflow  lowered  the  outlet,  and  with  this  lowering  the 
level  of  the  lake  was  gradually  drawn  down.  About  20  feet  above 
the  present  lake  its  level  remained  nearly  constant  long  enough 
to  allow  a  third  series  of  beaches  to  be  developed.  This  may  be 
called  the  fourth  stage  (the  Tolleston  stage)  of  the  lake.  • 

Still  later,  an  outlet  was  opened  to  the  north,  probably  as 
the  result  of  the  recession  of  the  ice.  This  outlet  was  lower  than 
that  via  Lemont,  and  the  level  of  the  lake  was  drawn  down  suffi- 
ciently 10  cut  off  the  flow  via  the  outlet.  When  this  was  done, 
the  present  conditions  were  inaugurated,  and  the  history  of  Lake 
Chicago  was  at  an  end. 


THE  BEACHES  OF  LAKE  CHICAGO. 

The  Upper  or  Glenwood  beach. — The  different  levels  at  which 
the  waters  of  Lake  Chicago  stood  for  any  considerable  length  of 
time  are  marked  by  a  series  of  well-defined  shore-lines,  whose 
ridges  of  beach  sand  and  gravel  have  been  mentioned  (p.  7)  as 
significant  features  of  the  Chicago  plain.  The  positions  of  the 
various  shore-lines  are  indicated  on  Plate  II  (p.  8),  and  in  Figs. 
14,  17  and  18.  As  before  stated,  the  water  at  first  rose  to  a  level 
about  60  feet  above  that  of  Lake  Michigan,  or  640  feet  above  sea 
level,  before  it  found  an  outlet,  and  at  this  level  was  formed  the 
first  and  highest  beach.      To  this  Mr.  Leverett  has  given  the  name 


34  THE  GEOGRAPHY  OF 

Glefnc'ooii,  from  the  village  of  Glenwood,  on  the  Chicago  and  East- 
ern  Illinois  railroad,  four  miles  south  of  the  Calumet  river.      At 


or  THt  VICINIT  ot 

CHICAGO 

AT  THE 

GLENWOOD  STAGE 
\ LAKE  CHICAGO. 

SHADED  AREA  LAND 


SCALL  or  MILES 


k^^ 


Fig.  14.    The  vicinity  of  Chicago  during  the  Glenwood  stage  of  Lake  Chicago.    The  area 
between  the  present  shore  and  the  shaded  area  was  covered  by  water. 


CHICAGO  AND  ITS  ENVIRONS.  35 

Glenwood  the  beach  is  especially  well  developed.  The  relations 
of  land  and  water  while  the  Glenwood  beach  was  forming  are 
shown  on  the  map  (Fig.  14). 

The  shore-line  corresponding  to  the  Glenwood  beach  extends 
an  undetermined  distance  northward  into  Wisconsin,  but  is  want- 
ing between  Winnetka  and  Waukegan,  where  the  present  lake 
shore  is  west  of  the  position  occupied  by  the  shore  of  Lake 
Chicago  when  the  Glenwood  beach  was  formed. 

The  northern  end  of  the  Glenwood  beach,  so  far  as  the 
environs  of  Chicago  are  concerned,  lies  on  the  crest  of  the  pres- 
ent bluff  near  Winnetka.  From  the  bluff  at  Winnetka  this  beach 
swings  southwestward  for  several  miles  to  Norwood  Park  (PI.  II, 
and  Fig.  14)  on  the  Wisconsin  division  of  the  Chicago  and  North- 
western railway.  Thence  its  course  is  southerly  through  Dun- 
ning County  Farm  and  Galewood,  to  a  point  about  one  mile 
south  of  the  Chicago,  Milwaukee  and  St.  Paul  railway.  Extend- 
ing northward  between  Galewood  and  Maywood  there  was  a  shal- 
low bay,  two  or  three  miles  in  width.  From  Maywood  the  beach 
swings  southwestward  and  southward  through  La  Grange  to  the 
line  of  the  present  Des  Plaines  valley,  near  McCook  Station, 
whence  it  makes  for  the  outlet  which,  at  this  stage,  was  about 
three  miles  southwest  of  McCook.  The  outlet  here  was  about 
one  mile  in  width. 

The  head  of  the  Sag  outlet  at  the  Glenwood  stage  was  about 
two  miles  west  of  the  village  of  Worth,  and  about  one-half  mile 
in  width.  From  the  Sag,  the  Glenwood  shore-line  passes  southeast- 
ward along  the  inner  slope  of  the  moraine,  which  rises  now  gently 
and  now  abruptly,  from  the  plain.  Passing  about  one-half  mile 
north  of  Homewood,  on  the  Illinois  Central  railroad,  the  shore 
extended  southeastward  through  Glenwood,  on  the  Chicago  and 
Eastern  Illinois  railroad. 

Just  southeast  of  Glenwood  the  beach  deposits  have  been 
almost  entirely  removed  by  the  erosion  of  Deer  creek,  but  one- 
half  mile  farther  on  the  beach  is  again  seen,  flanking  the  lake- 
ward  side  of  a  sharp,  narrow  ridge  of  drift.  Thence  it  runs  east- 
ward to  Dyer,  Indiana. 

The  Glenwood  shore-line  has  certain  features  which  deserve 
special  mention. 

Tlie   Oak  Park  spit. — From  Norwood  Park  south   to  the  Chi- 


36 


THE  GEOGRArilY  OF 


cago,  Milwaukee  and  St.  Paul  railroad  and  beyond,  the  old  shore- 
line lay  along  the  east  margin  of  a  moderately  high  and  slightly 
rolling  tract,  to  the  west  of  which  there  is  a  depressed  area  which 
was  a  shallow  bay  (Fig.  14),  two  or  three  miles  in  width,  at  the  time 
the  Glenwood  beach  was  formed.  In  the  western  part  of  this  low 
area  the  Des  Plaines  river  has  now  cut  its  channel.  As  there 
was  little  wave  action  in  the  bay  its  shore  lines  are  not  clearly 
marked. 

Across  the  debouchure  of  this  bay  the   shore  currents,    mov- 
ing southward    toward  the   outlet    under    the  influence   of  strong 

northeast  winds,  as  along  the 
west  shore  of  Lake  Michigan 
to-day,  gradually  built  out  the 
shore  drift  into  a  long,  narrow 
spit  (PI.  II  and  Fig.  15)  diag- 
onally across  the  mouth  of  the 
bay.  This  spit  (or  possibly  a 
barrier  beach)  passes  through 
Oak  Park,  terminating  at  For- 
est Home  Cemetery,  near  the 
Des  Plaines  river.  Its  double 
curve  is  probably  due  to  the 
combined  action  of  the  northeast 
winds  and  the  current  of  outward 
i^ow  from  the  bay.  The  former 
turned  the  spit  southwestward, 
until  the  outlet  of  the  bay  was 
somewhat  constricted,  when  the 
outward  flow  of  water  from  the 
north  became  sufficiently  strong 
to  deflect  the  spit-building  cur- 
rent again  to  the  south. 

The  method  of  building  a  spit 
is  readily  explained.     A  current 


l-ig. 


moved  along  the  shore  in  the  direction  indicated  by  the  arrows. 
While  flowing  on  the  shallow  bottom  near  shore,  the  current 
carried  along  more  or  less  sand  and  gravel.  As  it  reached 
the  point  of  land  below  Galewood,  it  continued  across  the  bay 
in  the  general    direction   already  assumed,   instead    of    following 


CHICAGO  AND  ITS  ENVIRONS.  37 

the  re-entrant  of  the  shore.  As  it  reached  the  deeper  and  more 
quiet  waters  opposite  the  mouth  of  the  bay,  its  velocity  was 
checked,  the  carrying  power  reduced,  and  the  load  dropped. 
More  material  was  constantly  brought  forward,  being  carried  out 
each  time  a  little  farther  over  the  deposit  already  made.  Thus 
the  narrow  submerged  ridge  of  sand  and  gravel  was  extended  out 
from  the  headland  in  the  direction  of  the  shore  currents. 

As  a  current  flows  across  the  mouth  of  the  bay,  the  sweep 
of  the  winds  across  the  open  water  of  the  lake  is  likely  to  deflect 
it  into  the  bay,  and  the  spit  receives  a  like  deflection.  If  turned 
in  sharply,  it  forms  a  hook.  If  the  process  of  spit-building  con- 
tinues until  the  opposite  shore  of  the  bay  is  reached,  the  bay  is 
completely  cut  off,  and  the  embankment  forms  a  bar.  When  it  is 
built  up  to  the  level  of  water  of  quiet  weather,  the  waves  of  storms 
may  throw  up  the  material  still  higher,  and  the  bar  becomes  the 
shore-line,  with  a  lagoon  shut  in  behind  it. 

The  tendency  to  cut  off  shallow  bays  by  means  of  spits  and 
bars  across  their  openings,  and  so  to  straighten  and  simplify  the 
shore-line,  is  one  common  to  all  bodies  of  standing  water. 

Cliff  and  zvave-cut  terrace. — North  of  McCook  the  shore  line 
is  marked  by  a  wave-cut  terrace.,  and  low  cliff,  cut  in  the  glacial  drift, 
rather  than  by  a  sandy  beach. 


Fig.  16.    Diagrammatic  section,  illustrating  the  formation  of  a  cliff  and  wave-cut  terrace. 

The  method  of  formation  of  a  cliff  and  wave-cut  terrace  is  as 
follows:  D  A  (Fig.  16)  is  a  land  surface  sloping  gently  to  a  lake, 
the  level  of  which  is  D'  A,  A  being  the  original  position  of  the  shore- 
As  the  waves  dash  against  the  shore,  the  bank  is  more  or  less  eroded, 
and  the  debris  is  either  washed  backward  by  the  undertow  and  spread 
on  the  bottom,  or  carried  along  the  shore  by  littoral  currents  to  be 


38  THE  GEOGRAPHY  OF 

deposited  wherever  motion  sufficient  for  its  transportation  fails.  As 
the  zone  of  greatest  erosion  is  at  the  water's  edge,  extending  a 
little  above  and  below  the  level  of  quiet  water,  the  shore  is  grad- 
ually cut  backward  as  with  a  horizontal  saw,  the  material  above 
sliding  and  falling  down  when  undercut,  and  being  worked  over 
and  carried  away  by  the  waves  and  currents.  Thus  with  a  surface 
rising  back  from  the  shore,  the  shore  grows  higher  as  the  water 
advances  on  the  land,  and  becomes  a  cliff,  while  the  bottom  of  the 
lake  near  shore  slopes  gently  up  to  the  water's  edge,  forming  a 
wave-cut  terrace.  The  horizontality  of  its  landward  margin,  which 
also  marks  its  junction  with  the  cliff,  is  the  especial  characteristic 
of  the  wave-cut  terrace.  It  should  be  noted,  however,  that  in  the 
case  of  the  ancient  terraces  from  which  the  lake  has  withdrawn, 
their  landward  margins  are  locally  rendered  uneven  by  alluvial 
fans  formed  at  the  debouchures  of  ravines  and  gullies  in  the  old 
lake  cliff. 

Dunes  of  the  Glenwood  beach. — One  mile  east  of  Homewood, 
the  beach  is  covered  by  dunes,  or  wind-blown  sand,  which  origi- 
nated later  than  the  beach  itself.  In  the  field,  the  shore  gravels 
are  seen  to  come  out  from  under  the  dune  sand,  and  to  extend  on 
toward  Glenwood. 

The  Glenwood  spit. — Southeast  of  Glenwood,  and  near  the  Illi- 
nois-Indiana line,  there  was  a  shallow  bay  (Fig.  14).  The  shore  cur- 
rents did  not  follow  the  shore  of  the  bay,  but  as  in  the  case  of 
the  bay  farther  north  near  Galewood,  they  swept  onward  across 
the  inlet,  bearing  the  shore  drift  of  sand  and  gravel  with  them. 
As  the  currents  came  into  deeper  water  across  the  opening  of  the 
bay,  they  dropped  their  burdens  of  detritus,  and  gradually  built  it 
out  into  a  great  spit  nearly  two  and  one-quarter  miles  in  length, 
almost  completely  shutting  off  the  bay  (see  PI.  II,  p.  8).  The  land- 
ward deflection  of  the  detritus-bearing  currents  by  easterly  winds 
is  well  illustrated  by  the  curved  form  of  the  spit.  In  quieter 
weather,  the  current  flow,  and  the  consequent  spit-building,  was 
southeastward  in  the  general  direction  of  the  shore-line,  but  during 
periods  of  heavy  storms  from  the  easterly  quarter,  the  currents 
were  deflected  into  the  bay,  and  the  spit  suffered  a  like  deflection. 
During  storms  the  distal  part  of  the  spit  was  probably  washed 
away,  and  the  material  swept  back  into  the  bay  in  the  form  of  a 
hook,    and  only  with    the  return  of   more   quiet   weather  was  the 


CHICAGO  AND  ITS  ENVIRONS.  '      39 

extension  of  the  spit  in  the  original  direction  resumed.  The 
structure  as  a  whole  is  that  of  a  great  curved  bar  formed  by  a 
series  of  hooks  extended,  one  from  the  other,  with  the  same 
general  front  (PL  II).  As  this  bar  increased  in  height  until 
it  stood  at  or  near  the  water  level,  it  became  the  real  shore-line, 
and  was  further  heightened  by  accumulations  of  dune  sand.  This 
ridge  has  now  a  height  of  15  feet  above  the  plain  to  the  north  and 
east. 

Duration  of  Glenwood  stage. — How  long  the  waters  stood  at 
this  upper  level  cannot  be  told,  but  it  was  long  enough  to  accom- 
plish considerable  erosion  of  the  outlet,  and  of  the  inner  margin 
of  the  moraine.  Most  of  the  debris  resulting  from  this  shore 
erosion  seems  to  have  been  swept  through  the  outlet,  instead  of 
being  deposited  on  the  lake  bottom. 

Changes  of  water  level. — The  level  of  the  lake  was  probably 
not  constaat  during  the  Glenwood  stage.  The  outlet  was  probably 
being  cut  down  continuously,  and  the  level  of  the  water  in  the  lake 
correspondingly  lowered.  How  much  it  had  been  lowered  before 
the  next  succeeding  stage  of  the  lake  was  inaugurated  is  unknown, 
but  there  is  some  reason  for  thinking  that  it  may  have  lowered 
something  like  20  feet.  As  the  water  level  became  lower,  the  level 
of  wave-cutting  was  correspondingly  lowered,  and  the  cutting  edge 
of  the  waves  was  felt  at  all  levels  successively  from  the  highest 
stand  of  the  lake  (640  feet)  to  the  lowest. 

Life. — No  satisfactory  evidence  of  life  has  been  found  in  the 
waters  of  the  lake  at  the  Glenwood  stage.  This  is  as  would  be 
expected  in  waters  mostly  derived  from  the  melting  of  the  great 
ice-sheet. 

Blue  Island. — Within  the  area  of  the  Chicago  plain  shown  on 
Plate  II,  and  within  the  area  of  that  part  of  Lake  Chicago  shown  in 
Figs.  I  and  14,  the  only  emerging  land  was  Blue  Island,  the  ridge 
of  drift  already  mentioned  (p.  7).  That  this  is  a  ridge  of  drift  and 
not  of  rock  covered  with  a  mantle  of  drift,  is  shown  by  well  bor- 
ings. The  well  at  Morgan  Park  Water  Works  shows  76  feet  of 
drift  overlying  the  rock,  while  the  well  at  the  Blue  Island  smelter, 
on  the  flat  about  one  and  one-quarter  miles  to  the  south,  shows  40 
feet  of  drift  over  the  rock.  The  difference  in  elevation  between 
the  two  points  is  such  as  to  show  that  the  surface  of  the  rock  has 
almost  the  same  level  under  the  ridge  as  under  the  flat. 


40  THE  GEOGRAPHY  OF 

There  seems  to  be  no  assignable  reason  why  excessive  depo- 
sition should  have  occurred  at  this  point.  It  is  probable  that  as 
left  by  the  ice,  this  elevation  of  drift  spread  out  to  the  east,  north 
and  south  somewhat  more  than  now,  with  more  gentle  slopes,  such 
as  now  occur  on  the  west.  If  this  be  true,  it  originall\'  formed  a 
broader  and  less  abrupt  swell  than  now. 

At  the  Glenwood  stage  of  the  lake,  this  drift  ridge  was  an 
island  rising  lo  to  35  feet  above  the  waters  of  Lake  Chicago.  On 
its  eastern  side  the  waters  developed  a  cliff,  and  the  debris  result- 
ing from  the  erosion  was  carried  out  some  slight  distance  from  the 
shore.  The  currents  toward  the  outlet  from  the  east  and  south- 
east appear  to  have  been  divided  by  the  ridge,  one  part  of  the 
water  sweeping  about  the  north  end,  and  the  other  part  about  the 
south.  These  currents  gathered  up  the  debris  which  the  waves 
developed,  and  swept  it  out  to  the  leeward  of  the  island  in  a  pair 
of  spits,  one  at  the  north  end  and  one  at  the  south  (Fig.  6).  That 
at  the  north  is  best  seen  at  the  Catholic  cemetery  at  Ste.  Maria 
on  the  Chicago  &  Grand  Trunk  Railway.  It  may  be  that  the 
accumulations  of  bowlders  at  the  north  end  of  the  Blue  Island 
ridge  are  a  remnant  from  this  erosion,  being  the  coarse  materials 
which  the  waves  and  currents  were  not  able  to  carry  away. 

The  deposits  of  sand  and  gravel  seen  just  east  of  the  till  ridge 
at  Morgan  Park,  Washington  Heights  and  elsewhere,  were 
probably  built  in  the  form  of  barrier  ridges  by  the  action "  of  the 
waves  and  currents.  The  beach  gravels  along  the  west  side  of  the 
island  are  buried  beneath  an  accumulation  of  dune  sand  which  was 
blown  up  later,  when  the  sandy  flat  to  the  west  emerged  from  the 
waters.  This  well-defined  dune  sand  deposit  gives  evidence  of 
prevailing  west  and  southwest  winds,  as  at  present. 

Interval  of  emergence. — After  the  Glenwood  beach  was  formed, 
a  northern  outlet  for  the  lake  seems  to  have  been  opened,  and  its 
level  was  lowered  until  the  waters  of  the  lake  receded  to  or  beyond 
the  present  shore-line  of  Lake  Michigan.  The  opening  of  the  north- 
ern outlet  was  probably  due  to  a  recession  of  the  ice-sheet  beyond 
some  valley  lower  than  the  Chicago  outlet.  As  before  stated,  the  evi- 
dence of  the  emergence  of  the  Chicago  plain  at  this  time  is  found  in 
a  bed  of  peat  beneath  the  deposits  of  the  succeeding  stage,  showing 
that  the  waters  must  have  withdrawn  from  the  plain  for  a  time  suf- 
ficiently long  to  allow  vegetation    to   grow  and  accumulate  before 


CHICAGO  AND  ITS  ENVIRONS.  41 

the  area  was  re-submerged,  and  the  later  deposits  formed.  These 
deposits  were  best  seen  some  years  ago  in  a  section  on  the  campus 
of  Northwestern  University  in  Evanston.  Further  evidence  con- 
cerning this  interval  of  emergence  is  desired.  Recent  investiga- 
tion has  not  discovered  new  data  bearing  on  the  subject,  which 
remains  as  set  forth  by  Dr.  Andrews  years  ago,  and  more  recently 
by  Mr.  Leverett. 

The  Calinnet  beach.- — Following  the  period  of  emergence,  the 
waters  of  Lake  Chicago  again  rose  and  flooded  the  Chicago  plain. 
This  re-submergence  may  have  been  due  to  a  return  of  the  glacier 
ice  to  the  northern  end  of  the  basin,  blocking  the  outlet  which  had 
been  opened  to  the  north,  or  to  a  rise  of  the  land  in  that  direction, 
lifting  the  outlet  and  causing  the  water  in  the  lake  to  rise.  The 
height  to  which  the  water  rose  in  the  second  submergence  of  the 
Chicago  plain  is  marked  by  the  second  or  Calumet  beach,  about  35 
to  40  feet  above  the  present  lake,  and  about  20  feet  below  the 
beach  of  the  Glenwood  stage.  It  is  the  rise  to  this  level,  and  not 
higher,  which  suggests  that  the  water  of  the  Glenwood  stage  had 
been  drawn  down  about  20  feet  by  the  lowering  of  the  outlet  (p.  iq). 

Like  the  older  beach,  this  lower  and  younger  one  has  its 
correlative  in  Wisconsin.  It  h3.s  been  recognized  25  miles  north 
of  Milwaukee,  but  from  this  latitude  southward  to  a  point  between 
Racine  and  Kenosha,  a  distance  of  more  than  50  miles,  it  has  been 
cut  away  by  the  advance  of  the  lake  on  the  land  in  later  times. 
From  the  Wisconsin  line  southward  to  the  Chicago  river,  the  sec- 
ond beach  is  closely  associated  with  the  first,  wherever  the  first 
remains. 

South  of  the  North  Branch  of  the  Chicago  river,  the  Calumet 
beach  is  seen  in  good  development  at  Jefferson  Park  (Fig.  17). 
Thence  it  runs  through  Cragin,  to  Austin  and  Riverside.  Through 
this  distance  of  12  miles  there  is  a  continuous  well-developed 
beach  ridge  of  sand  and  gravel. 

At  this  stage  of  the  lake,  the  drainage  of  the  region  northwest 
of  its  border,  along  the  line  of  the  Des  Plaines  river,  and  probably 
along  the  line  of  Salt  creek,  entered  the  lake  between  Riverside 
and  the  rock  elevation  at  Lyons. 

From  Riverside  to  the  outlet,  the  head  of  which  at  this  stage 
was  at  Summit,  the  Calumet  shore-line  is  not  well  defined. 

At  the  Calumet  stage  of  the  lake,  the  Mount  Forest  and  Blue 


42  THE  GEOGRAPHY  OF 

Island  islands  of  the  Glcnwood   stage  were  no  longer  separate,  for 
the  plain   between   them  was  above  water.      These  islands  of   the 


Fig.  1".    The  Calumet  stage  of  Lake  Chicago.    The  unshaded  area  west  of  the  present  lake  \vas 
covered  by  water.    The  figure  also  shows  the  position  of  the  Glcnwood  beach. 


CHICAGO  AND  ITS  ENVIRONS.  43 

Glenwood  stage,  and  the  area  between  them  now  formed  one  large 
island  between  \he  two  outlets.  Sag  Station  marks  its  western 
extremity,  Summit  the  northern,  and  Blue  Island  village  the  south- 
eastern. 

From  Summit,  the  shore-line  of  the  Calumet  stage  swung  in  a 
broad  curve  southeastward  about  the  north  end  of  the  Blue  Island 
ridge,  through  Washington  Heights.  Throughout  this  distance  of 
eleven  and  one-half  miles,  the  Calumet  beach  is  marked  by  a  con- 
tinuous, well-developed  ridge  of  sand  and  gravel,  five  to  ten  feet 
high,  and  50  to  100  yards  wide.  From  Washington  Heights  to  the 
town  of  Blue  Island,  the  outer  of  the  barrier  ridges  mentioned  (p. 
40)  marks  the  shore-line  of  this  stage. 

The  head  of  the  Sag  outlet  at  this  stage  may  be  considered  as 
lying  between  the  south  end  of  the  Blue  Island  ridge  and  the 
inner  margin  of  the  moraine  three  miles  farther  south-west. 
If  this  be  considered  the  head  of  the  outlet,  the  water  passing 
through  it  was  divided  into  two  currents  b}'  a  low  body  of  land 
known  as  Lane's  Island.  The  area  of  this  island  was  submerged 
in  the  Glenwood  stage,  but  the  lower  water  of  the  Calumet  staare 
left  the  crest  of  the  low  ridge  exposed.  The  village  of  Worth,  on 
the  Wabash  Railway,  stands  at  its  western  end.  The  present 
Stony  creek  canal  feeder  now  follows  the  course  of  the  channel 
which  lay  to  the  north  of  this  island. 

From  the  south  side  of  the  Sag  outlet  to  the  rock  elevation  at 
Thornton,  the  Calumet  shore-line  was  almost  parallel  to  that  of 
the  preceding  stage,  and  but  about  one-half  mile  inside  it.  The 
line  is  here  marked  by  a  continuous  ridge  of  beach  sand  and 
gravel.  After  swinging  to  the  northward  about  the  Thornton  ele- 
vation, this  ridge  continues  eastward  into  Indiana. 

Between  Homewood  and  Thornton  there  is  a  considerable 
deposit  of  dune  sand,  in  hillocks  20  to  30  feet  in  height,  now  well 
covered  by  vegetation.  These  dunes  overlie  part  of  the  beach 
deposits  of  the  Glenwood  stage.  The  eolian  sand  which  overlies 
the  Glenwood  beach  may  have  originated  at  any  time  subsequent 
to  the  formation  of  that  beach;  but  that  which  overlies  the  Calumet 
beach  must  belong  to  the  Calumet  or  to  some  later  stage.  There 
is  also  much  dune  sand  associated  with  the  Calumet  beach  east  of 
Thornton. 

Rose  Hill  bar. — From  the  Calumet    beach,   north  of  Chicago, 


44  THE  GEOCRA  Pit Y  OF 

there  extended  into  the  Chicago  embayment  at  this  stage  a  con- 
spicuous bar  (PI.  II).  Its  northern  end  is  found  at  the  present 
lake  shore  between  Wilmette  and  Evanston.  Its  connection 
with  the  old  shore-line  has  been  cut  away  by  the  advance  of 
the  lake  on  the  land.  It  runs  southward  through  the  western 
part  of  Evanston,  and  on  it,  near  its  southern  extremity,  is  Rose 
Hill  Cemetery.  It  is  beneath  this  bar  that  the  peat  deposits  which 
give  the  evidence  of  an  interval  of  emergence  between  this  and 
the  Glenwood  stage  of  the  lake,  were  found. 

Evidence  of  life  in  the  lacustrine  deposits  of  the  Cahimct  stage.  — 
In  connection  with  the  evidence  of  a  withdrawal  of  the  water  from  the 
Chicago  plain  at  the  close  of  the  Glenwood  stage,  and  its  conse- 
quent submergence  by  the  waters  of  the  Calumet  stage,  the  find- 
ing of  evidences  of  life  in  these  lake  deposits  is  of  especial  interest. 
The  occurrence  of  shells  in  the  Calumet  beach  deposits  at  Summit 
and  near  New  Buffalo,  Michigan,  has  been  reported,  but  no  definite 
information  has  been  secured  concerning  them.  The  only  place 
where  definite  evidence  of  life  has  been  found  about  Chicago  is  at 
the  farm  of  Mr.  J.  H.  Welch,  about  one  and  one-half  miles  southwest 
of  Chicago  Lawn.  The  Calumet  shore-line  was  spoken  of  as  being 
marked  by  a  well-developed  ridge  of  sand  and  gravel  swinging  in 
a  broad  curve  from  Summit  southeastward  about  the  north  end 
of  the  Blue  Island  ridge.  In  Mr.  Welch's  field,  just  northwest  of 
the  point  where  this  ridge  is  cut  by  the  Belt  railway,  there  have 
been  found  numerous  molluscan  shells,  and  one  specimen  of  coral. 
An  examination  of  these  specimens  showed  them,  without  excep- 
tion, to  be  of  marine  species,  whose  present  range  is  between 
Prince  Edward  Island  and  the  West  Indies.'  With  the  specimens 
which  could  be  identified  there  were  many  fragments  so  well  worn 
and  so  thoroughly  perforated  as  not  to  permit  of  identification. 
The  character  of  the  evidence  which  these  shells  seem  to  afford  is 

'Tlie  species  as  identified  by  Mr.  Frank  C.  liaker  of  the  Cliicagfo  Academy  of  Sciences, 
are  as  follows: 

Pelecypods:  Ostrea  virginica  Gmelin,  ranging  at  present  from  Prince  Edward  Island 
to  the  West  Indies.  These  specimens  are  very  largely  perforated  by  boring  sponges.  Area 
transversa  Linnc.  ranging  from  Cape  Cod  to  Key  West.  Venus  cancellata  Linne,  ranging 
from  Cape  Hatteras  to  Trinidad.  Venus  mercinariiis  {})  Linne.  Pecten  (Sp.  ?)  possibly 
CItlamys  irradians  Linne,  a  fragment.    Gnathodon  cuneatu^  Gray,  Gulf  of  Mexico. 

Gastropods:  Fulgar  pcrversus  Linne,  ranging  from  Cape  Hatteras  to  Cuba.  Cerith- 
iutn  (Sp.  ?),  apical  whorls  only  found.     Cerithiopsis  (Sp.  ?)    apical  whorls  only  found. 

Coral:     Oculina  robusta  Pourtales,  West  Indies. 


CHICAGO  AND  ITS  EiWIRONS.  45 

of  such  a  radical  nature  as  to  excite  great  interest,  and  conclusions 
must  be  drawn  with  extreme  caution. 

The  question  is,  were  the  shells  left  in  their  present  position 
by  natural  agencies?  To  say  that  they  reached  their  present  posi- 
tion by  natural  means,  is  to  say  that  the  waters  of  Lake  Chicago 
at  the  Calumet  stage  were  salt.  This  would  seemingly  require  the 
subsidence  of  this  and  surrounding  areas  to  such  a  level  as  would 
allow  the  incursion  of  the  sea  over  this  part  of  the  interior  of  the 
continent,  and  their  subsequent  elevation  to  the  present  altitude 
of  620  feet  above  tide,  within  very  recent  geological  time. 

It  is  true  that  this  is  not  the  first  or  only  suggestion  of  such 
a  subsidence  and  marine  incursion.  Dr.  R.  W.  Ells'  of  the  Geo- 
logical Survey  of  Canada,  has  recently  brought  forward  evidence 
to  show  that  the  ocean  extended  westward  throughout  the  upper 
Ottawa  basin  in  post-glacial  time,  leaving  marine  deposits  which 
are  now  1,000  feet  above  the  sea  level.  Dr.  Bell'^also  records  the 
presence  of  marine  deposits  north  of  Lake  Superior,  along  the 
Kenogami  river,  at  an  elevation  of  450  feet  above  sea  level.  It  is 
not  unreasonable  that  the  subsidence  of  the  area  about  Chicago 
should  have  occurred  as  a  part  of  the  more  general  subsidence  of 
which  these  marine  deposits  to  the  north  and  northeast  seem  to 
be  evidence. 

There  also  occur  along  the  lake  shore  certain  plants,^  long 
regarded  as  seashore  plants,  and  these,  together  with  the  existence 
of  a  Mysis,  a  species  of  marine  crustacean,  in  the  lake,  have  been 
taken  as  evidence  that  salt  water  has  at  some  time  existed  where 
Lake  Michigan  now  is."* 

iDr.  R.  \V.  Ells.  Sands  and  Clays  of  the  Ottawa  Basin.  Bull.  Geol  Soc.  Am.,  Vol.  IX, 
pp.  211-222,  February,  iSgS. 

-Report  of  Progress,  Canadian  Geol.  Surv.,  1895,  Vol.  VI,  p.  340. 

^These  plants  are  Triglochin  mari/ima  (arrow  grass) ;  Sa/sola  i'ali  (Kussia.T\  thistle); 
Cakile  americana  (sea  rocket);  Prunus  mantima  (beach  plum);  Lathyrus  mnritimus  (beach 
pea);  Euphorbia  ■pohgonifoLta  (seaside  spurge). 

This  list  of  plants  is  kindly  furnished  by  Dr.  H.  C.  Cowles  of  the  University  of  Chicago. 
It  should  be  stated,  however,  that  Dr.  Cowles  gives  little  credence  to  them  asevidence  of  marine 
conditions  here,  rather  considering  it  as  begging  the  question  to  regard  plants  with  such  a  wide 
range  along  the  interior  lake  shores  as  strictly  sea-shore  plants. 

*The. Flora  of  Cook  County,  Illinois,  and  a  part  of  Lake  County,  Indiana.  Wm.  K.  Hig- 
ley  and  Charles  S.  Raddin,  Bull.  Chicago  Acad.  Sci.,  Vol.  II,  No.  i,  p.  15.  iSgi. 


46  THE  GEOCRArHY  OF 

The  presence  of  the  fossils  mentioned  above  might  be 
accounted  for  by  artificial  introduction.  They  might  have  been 
thrown  there  by  white  men,  or  introduced  in  a  fertilizer  used  on 
the  soil.  The  well-known  trading  of  the  Indians  of  the  northern 
interior  with  the  south  and  east  coast  might  account  for  their  hav- 
ing been  left  here,  before  the  coming  of  white  men.  They 
might  have  been  left  on  the  beach  of  Lake  Chicago  by  the  Indians 
of  that  time,  and  have  been  water-worn  and  buried  by  the  waves 
of  its  shore.  It  should  also  be  noted  that  the  physical  relations 
indicate  that  the  Calumet  beach  marks  the  border  of  a  lake  which 
seems  to  have  stood  sufficiently  above  sea  level  to  maintain  a 
strong  current  through  its  outlet,  which  seems  incompatible  with 
the  occurrence  of  marine  life  in  its  waters. 

On  the  other  hand,  the  water-worn  and  fragmental  condition 
of  a  large  part  of  the  marine  shells  found  on  the  Calumet  beach, 
the  thorough  perforation  of  many  specimens  by  sea-borers,  the 
occurrence  of  very  delicate,  tiny  shells  in  the  sand  filling  the  coils 
of  the  larger  gasteropod  shells,  together  with  the  statements  of 
Mr.  Welch,  that  he  himself  cleared  the  ridge  of  its  native  trees 
and  underbrush,  broke  the  sod,  and  has  lived  there  for  nearly 
thirty  years,  that  he  never  used  any  fertilizer  containing  shells, 
that  the  only  evidence  of  Indian  residence  he  has  ever  found  was  a 
single  arrowhead,  that  he  has  plowed  up  and  gathered  the  shells 
ever  since  the  ground  was  broken — all  these  facts  are  against  the 
idea  of  an  artificial  introduction  of.the  shells,  and  favor  the  idea  of 
deposition  in  situ  by  marine  waters.  The  southern  range  of  all  the 
species  found  would  also  seem  to  preclude  the  idea  of  their  intro- 
duction from  the  north  or  northeast,  for  the  shells  found  by  Drs. 
Bell  and  Ells  are  all  of  Arctic  species.  If  the  shells  be  evidence 
of  an  incursion  of  the  sea,  their  occurrence,  so  far  as  known  on 
this  second,  or  Calumet  beach  only,  would  indicate  this  stage  (or  a 
part  of  it)  as  the  time  of  the  incursion,  and  the  southern  range  of 
all  these  species  at  the  present  day  would  indicate  that  the  incur- 
sion was  not  from  the  northeast  through  the  St.  Lawrence  embay- 
ment,  but  from  the  south,  through  a  Mississippi  embayment. 

In  view  of  these  apparently  conflicting  considerations,  final 
judgment  concerning  the  interpretation  of  the  shells  must  be  sus- 
pended until  further  evidence  is  forthcoming. 

7'hc  Third  or  Tollcston  beach. — Following  the  Calumet  stage  of 


CHICAGO  AND  ITS  ENVIRONS. 


47 


the  lake  was  a  stage  during  which   the  waters  stood  at  a  level  but 
20  feet  above  the  present  lake.      The  lowering  of  the  lake  from  the 


Fig.  18.    Shows  the  relations  of  land  and  water  about  Chicago  at  the  Tolleston  stage  of 
Lake  Chicajfo.    Shaded  areas,  land. 


48  THE  GEOGRAPHY  OF 

preceding  stage  may  have  been  due  to  a  re-opening  of  the  outlet 
to  the  north,  or  to  a  rapid  cutting  down  of  the  outlet.  The 
change  of  level  may  have  been  less  sudden  than  the  position  of 
the  two  shore-lines  might  lead  us  to  infer. 

At  this  stage  of  the  lake  a  third  beach  was  developed,  called 
the  Tolleston  beach,  from  the  village  of  Tolleston  in  northwestern 
Indiana.  The  relations  of  land  and  water  at  this  stage,  so  far 
as  the  vicinity  of  Chicago  is  concerned,  are  shown  in  Fig.  i8. 

Remnants  of  a  terrace  at  a  level  corresponding  to  this  shore- 
line have  been  seen  at  various  points  in  Wisconsin.  Such  a  ter- 
race has  been  seen  north  of  Milwaukee,  but  between  Milwaukee  and 
Kenosha,  it  has  been  destroyed  by  the  encroaching  of  the  lake  on  the 
laud.  From  Kenosha  to  Waukegan  it  is  well  developed,  and  is  fol- 
lowed closely  by  the  line  of  the  Chicago  and  Northwestern  railway. 
Thence  southward  to  Evanston,  the  advancing  shore  of  the  lake 
has  removed  all  trace  of  this  beach,  as  of  those  of  the  earlier 
stages.  At  Evanston,  on  the  grounds  of  the  Northwestern  Uni- 
versity, this  beach  appears  at  the  present  shore-line,  and  runs 
southward  along  the  eastern  border  of  the  Rose  Hill  bar  formed 
at  the  preceding  stage  of  the  lake  (PI.  II,  p.  8). 

The  low  area  to  the  west  of  Rose  Hill  was  probabl}^  flooded 
for  a  time  at  this  stage,  but  the  shore-line  from  Rose  Hill  to 
near  Hawthorne  is  poorly  marked.  Traces  of  it  are  seen  near 
Milwaukee  avenue  and  North  avenue,  at  the  rock  elevation  near 
the  intersection  of  Chicago  and  Western  avenues,  and  south- 
westward  from  the  corner  of  Douglas  and  Central  Park  boule- 
vards. From  the  rock  elevation  at  Hawthorne,  however,  which 
marks  the  north  side  of  the  head  of  the  outlet  at  this  stage,  to 
the  Des  Plaines  river  one  mile  north  of  Summit,  the  shore  of 
the  Tolleston  stage  of  the  lake  is  well  defined  by   a  sandy   beach. 

From  Summit  toward  Willow  Springs,  the  shore  of  the  outlet 
at  this  stage  is  marked  by  the  fifteen  to  twenty-foot  drift  bluff 
now  followed  by  Archer  road.  From  Summit  eastward,  the 
south  shore  of  the  outlet,  is  marked  by  a  low  bluff.  From  one- 
half  mile  west  of  the  corner  of  Western  avenue  and  Garfield  boule- 
vard, the  shore-line  is  marked  by  a  strong  ridge  of  sand  and  gravel 
which  swings  in  a  broad  curve  southeastward  through  Auburn 
Park  to  South  Englewood. 

In  the  earlier  j)art  of  the  Tolleston  stage  the  shore-line  seems 


CHICAGO  AND  ITS  ENVIRONS. 


49 


to  have  swung  off  to  the  south  and  southeastward  from  near  the 
intersection  of  South  Halsted  and  Eighty-seventh  streets,  and 
passing  through  Fernwood  at  Stewart  avenue  and  One  Hundred 
and  Third  street,  turned  southward  along  the  drift  cliff,  passing 
through  Kensington  to  the  Calumet  river  at  Riverdale.  The  Sag 
outlet,  probably  not  a  very  active  line  of  discharge  at  this  stage, 
seems  to  have  occupied  the  present  line  of  the  Calumet  river 
(reversed)  between  Riverdale  and  Blue  Island.  The  head  of  the 
outlet  was  narrow,  and  seems  soon  to  have  been  blocked  by  a 
bar  formed  from  material  borne  by  the  shore  currents  southward 
along  the  Kensington  cliff. 

West  of  Blue  Island  the  channel  was  divided  as  before  by 
Lane's  Island,  now  considerably  enlarged  by  the  lowering  of  the 
surrounding  waters. 

From  Dolton,  southeastward  into  Indiana,  the  shore-line  is 
marked  by  extensive  deposits  of  beach  sand  and  gravel,  now  much 
covered  by  accumulations  of  dune  sand. 

From  the  position  of  Rose  Hill  cemetery,  where  the  Rose 
Hill  bar  was  deflected  to  the  southwest,  the  shore  currents  con- 
tinued southward,  depositing  their  material  in  a  great  reef  o-wer 
most  of  that  part  of  the  North  Side  of  the  City  of  Chicago  which 
lies  between  the  North  Branch  of  the  Chicago  river,  and  the  pres- 
ent shore  of  Lake  Michigan  (Fig.  6,  p.  15).  The  slight  elevation 
which  this  deposit  made  is  traversed  by  North  Clark  street,  and 
about  midway  of  its  length  is  Graceland  cemetery. 

As  this  broad  reef-like  deposit  extended  southward  and  increased 
in  height,  it  finally  became  the  shore-line,  cutting  off  whatever  bay 
lay  to  the  west.  This  reef  is  readily  traceable  to  a  point  about  a 
mile  south  of  Lincoln  Park.  It  is  said  to  have  been  nearly  continu- 
ous through  the  City  of  Chicago,  but  it  is  now  scarcely  recognizable 
for  a  distance  of  nearly  four  miles  to  the  southward.  In  this  stretch, 
grading  has  destroyed  it ;  but  from  Groveland  Park,  at  Cottage 
Grove  avenue  and  Thirty-fourth  street,  it  extends  southwestward 
a  distance  of  seven  miles  through  the  northwestern  part  of  Wash- 
ington Park,  Englewood  and  Auburn  Park,  to  South  Englewood, 
where  it  unites  with  the  shore-line  just  described. 

This  broad  reef  appears  to  have  been  built  southwestward  as  a 
series  of  overlapping  hooks  which  were  turned  into  the  bay  at  the 
west  in  the  manner  already  described  (p.  36). 


50  THE  GEOGRAPHY  OF 

The  advance  of  the  reef  constricted  the  channel  of  free  flow 
toward  the  outlet,  and  the  drainage  in  that  direction  was  shifted 
more  and  more  to  the  south.  At  the  same  time  the  lowering  of 
the  lake  level  seems  to  have  diminished  the  outflow  in  that  direc- 
tion, so  that  the  current  was  feeble,  and  finally  destroyed,  and  the 
bar  was  completed  across  the  bay  to  the  farther  shore  at  South 
Englewood  (Fig.  i8).  This  is  the  most  notable  instance  within  the 
area  studied  of  the  process  of  cutting  off  embayments,  and  the  con- 
sequent simplification  of  the  shore-line.  The  southern  part  of  the 
area  behind  (west  of)  this  bar  eventually  drained  out  to  the  east- 
ward through  the  depression  now  occupied  by  the  Auburn  Park 
lagoon,  and  the  establishment  of  the  Chicago  river  probably  drained 
the  remainder. 

It  was  probably  while  this  reef  was  being  built  and  the  over- 
flow to  the  west  diminished,  that  the  present  outlet  of  the  lake  to 
the  north  was  being  established.  As  the  outflow  to  the  north 
increased,  that  via  Summit  diminished. 

At  the  Tolleston  stage  of  the  lake.  Stony  Island  had  begun  to 
emerge  as  an  island  or  a  reef  (Fig.  i8),  and  its  position  gave  it  a 
controlling  influence  on  the  currents.  Under  its  protection,  the 
currents  shifted  southward  by  the  extension  of  the  reef  already 
referred  to  began  to  work  upon  the  gentle  drift  slope  of  the  land 
along  the  west  shore  of  the  lake,  and  a  low  terrace,  surmounted 
by  a  sandy  beach,  was  developed  from  South  Englewood,  through 
Burnside  to  the  lee  of  Stony  Island.  These  southeasterly  currents 
were  here  met  by  the  westward  currents  about  Stony  Island,  and 
turned  abruptly  southwestward  toward  the  present  site  of  Pullman. 
As  a  result  of  the  reefs  made  by  these  currents,  the  shore-line  was 
shifted  eastward,  and  the  original  line  through  Fernwood  was 
abandoned. 

Stony  Island, — Stony  Island  is  an  elevation  of  rock.  Its  strata 
have  quaquaversal  or  periclinal  dips,  /.  e.,  the  strata,  on  all  sides 
of  the  ridge,  dip  outward  (Fig.  7).  The  angle  of  dip  ranges  from 
30°  to  42 '\  At  first  thought,  the  "island"  appears  not  to  be  an 
erosion  remnant,  but  due  to  a  local  elevation  of  the  rock  strata. 
Gentle  undulations  of  the  rock-beds  are  seen  at  other  exposures, 
but  none  so  abrupt  as  this.  No  very  satisfactory  evidence  is  at 
hand  by  which  the  date  of  the  uplift  which  deformed  the  beds  can 
be, fixed.      If    it    preceded    the    later  part    of    the    erosion   which 


CHICAGO  AND  ITS  ENVIRONS.  51 

affected  the  limestone  before  the  glacial  period,  the  erosion  rem- 
nant (that  is,  the  island)  happened  to  correspond  in  position  with 
the  center  of  the  uplift.  There  is  some  evidence  in  the  rock  itself 
that  its  deformation  took  place  while  the  layers  which  are  now 
exposed  were  under  great  weight.  If  this  be  so,  the  great  weight 
was  probably  the  weight  of  other  beds  since  eroded  away. 

The  large  island  to  the  west  of  Stony  Island. — The  large  island 
of  the  Calumet  stage,  made  by  the  union  of  the  Blue  Island  and 
Mount  Forest  islands  of  the  Glenwood  stage,  was  still  larger  dur- 
ing the  Tolleston  stage  (Fig.  18.  Compare  Figs.  14  and  17).  This 
was  the  necessary  result  of  the  lowering  of  the  waters  of  the  lake. 

Evidences  of  life  at  the  Tolleston  stage. — In  striking  contrast 
with  the  Glenwood  and  Calumet  beaches,  the  Tolleston  beach  con- 
tains abundant  traces  of  life  closely  related  to  the  life  of  Lake 
Michigan,  if  not  identical  with  it. 

Changes  in  topography  effected  by  Lake  Chicago. — Aside  from 
the  phenomena  of  the  shore-lines  set  forth  in  the  preceding  pages, 
certain  changes  in  the  topography  of  the  Chicago  plain  were 
effected  by  the  waters  of  Lake  Chicago. 

First  and  last,  the  level  of  Lake  Chicago  fluctuated  from  its 
maximum  640  A.  T.  to  the  present  level  of  Lake  Michigan, 
581  feet  A.  T.  The  shore  was  at  some  time  or  other  at  all 
levels  between  these  extremes,  and  the  horizontal  cutting  of  its 
waves  therefore  affected  all  parts  of  the  Chicago  plain.  By  this 
cutting,  the  inequalities  of  the  surface  of  the  drift  of  the  plain,  as 
left  by  the  ice,  were  almost  entirely  obliterated,  changing  a  plain 
that  was  at  least  slightly  undulating,  to  one  which  is  exceptionally 
flat.  The  Blue  Island  ridge  was  doubtless  the  highest  drift  swell, 
and  was  not  entirely  removed,  though  probably  much  narrowed  by 
the  waves.  During  the  Glenwood  stage  of  the  lake,  the  Val- 
paraiso moraine  was  cut  back  to  its  present  position,  leaving  the 
lake  plain  with  a  border  which  is,  in  many  places,  abrupt.  Most 
of  the  debris  resulting  from  the  erosion  of  the  shores  of  the  lake 
was  carried  out  through  the  outlet,  though  some  of  it  is  seen  in  the 
beaches,  and  some  of  it  was  spread  as  stratified  drift  over  certain 
parts  of  the  plain. 


52  THE  GEOGRAPHY  OF 

RECENT    CHANGES. 

Lake  Michigan  beach. — With  the  diversion  of  the  waters  of 
the  lake  from  the  outlet  to  the  north,  the  history  of  Lake  Chicago 
may  be  considered  as  passing  into  the  history  of  Lake  Michigan, 
so  that  the  series  of  beaches  and  bars  lying  between  the  Tolleston 
shore-line  of  Lake  Chicago  and  the  present  shore  of  Lake  Michi- 
gan, mark  the  closing  stages  of  the  history  of  Lake  Chicago,  and 
the  earliest  stages  of  Lake  Michigan.  During  this  stage,  sO  much 
of  the  Chicago  plain  as  was  still  submerged  was  being  built  up  by 
deposits  of  sand  and  gravel  brought  to  the  head  of  the  lake  by  the 
southward  drift  of  the  littoral  currents.  In  the  northern  part  of 
the  city,  as  far  south  as  Lincoln  Park,  there  is  a  close-set  series  of 
sand  and  gravel  ridges  lo  to  15  feet  high,  between  the  Tolleston 
beach  and  the  present  shore  of  the  lake.  These  ridges  are  often 
capped  with  a  little  dune  sand.  Southward  from  Thirty-fifth 
street  (PI.  II)  the  deposits  of  this  stage  cover  a  considerable  area. 
Northeast  and  east  of  Washington  Park,  there  is  a  series  of  10  to 
12  low  ridges.  These  were  built  as  subaqueous  ridges  by  drift 
from  the  north.  They  have  a  generally  parallel  direction,  some- 
times branch,  and  vary  in  length  from  one  to  six  miles,  running 
out  into  the  sandy  plain.  Their  southern  ends  are  usually 
turned  slightly  to  the  west,  as  in  hook  formations.  The  longest 
and  most  prominent  of  these  ridges  is  that  passing  through  the 
campus  of  the  University  of  Chicago,  where  its  structure  was  well 
seen  before  destroyed  by  grading.  It  continues  southward  through 
the  western  part  of  Oakwood  cemetery,  terminating  one  mile  north 
of  Burnside. 

The  existence  of  the  basin  of  Lake  Calumet  is  probably  due,  in 
part,  to  the  influence  of  Stony  Island  which  deflected  the  currents 
about  its  eastern  end,  whence  they  continued  southward,  depositing 
sand  and  gravel  along  their  course,  and  leaving  the  area  of  the 
shallow  lake  unfilled.  Like  ridges  enclosed  Hyde  Lake,  Wolf  lake 
and  Lake  George  (PI.  II),  as  well  as  the  adjacent  marshy  areas. 

Between  these  lakes  and  the  Tolleston  beach  to  the  south  is  a 
remarkable  series  of  parallel  ridges,  so  closely  set  that  they  can- 
not all  be  separately  represented  on  the  map.  Including  those 
indicated  on  the  map  as  belonging  to  the  Tolleston  stage,  there 
are,  from  Hammond  north  to  the  south  end  of  Lake  George,  90  of 
these  ridges,  ranging  from  three  to  ten   feet  in   height.      They  are 


CHICAGO  AND  ITS  ENVIRONS. 


53 


separated,  in  many  cases,  by  narrow  marshy  belts.  The  ridges 
running  southward  between  these  lakes  break  up  into  several  nar- 
row ridges,  and  curve  to  the  eastward  to  form  a  part  of  the  whole 
series.  These  ridges  are  composed  of  sand  with  little  gravel,  and 
taken  together  have  the  form  of  a  great  depositional  terrace. 
This  extensive  filling,  together  with  a  slight  lowering  of  the  water 
level,  brought  the  lake  shore  to  its  present  position.  The  drift  of 
the  sand  at  the  head  of  the  lake  and  its  accumulation  there  is  still 
in  progress. 

Shore  erosion. — The  opposite  phase  of  lake  shore  work, 
namely,  wave  erosion,  is  also  well  shown  near  the  city.  From 
Evanston  northward,  the  waves  of  the  lake  are  cutting  into  the 
bluffs,  and  driving  the  shore-line  farther  and  farther  west  (Fig.  i6). 
Locally  and  very  recently  this  advance   of  the  water   on  the  land 


Fig.  19.    Ulitt  on  the  shore  near  ijlencoe.    There  is  a  narrow  beach  at  the  base  of  the  clitt.    (Harms.) 

has  been  stayed  by  various  human  devices,  but  the  process  by 
which  cliffs  and  wave-cut  terraces  are  developed  is  still  clearly 
shown.  Fig.  16  illustrates  the  changes  which  have  taken  place 
where  the  shore  of  the  lake  is  a  bluff.  The  surface,  as  left  by  the 
ice,  occupied  some  such  position  as  A  D.  The  waves  have  cut 
back,  reaching  the  bluff  at  D'.  This  is  bordered  by  a  submerged 
wave-cut  terrace  to  the  right  of  D'. 


THE  GEOGRAPHY  OF 


CHICAGO  AAD  ITS  ENVIRONS. 


55 


Fig.  21.  Figure  illustrating  changes  in  the  position  of  the  debouchure  of  the  Chicago  river. 
The  position  of  the  outlets  in  1S30,  and  at  the  present  time,  are  shown,  and  also  the  posi- 
tion of  the  sand-bar  which  caused  the  deflection.-(Adapted  from  map  of  Col.  T.J.  Crane, 
U.  S.  Corps  of  Engineers.) 


56 


THE  GEOGR.IP//V  OF 


CHICAGO  AND  ITS  ENVIRONS. 


57 


58 


THE  GEOGRAPHY  OF 


The  material  eroded  by  the  waves  from  the  bluffs  has  been 
shifted  southward.  The  fact  of  this  southerl}'  transportation  may 
be  seen  on  the  north  side  of  every  pier  extending  into  the  lake, 
and  in  the  spits  wrapping  around  the  ends  of  these  piers  from 
north  to  south  below  the  water  surface. 

As  at  earlier  stages  in  the  history  of  the  lake,  so  now,  bars 
are  constantly  forming  across  the  river  mouths,  and  must  be 
repeatedly  removed  by  dredging  to  keep  the  harbors  open.  Before 
the  improvement  of  the  present  harbor  at  Chicago  there  was  a  bar 
across  the  outlet  of  the  Chicago  river,  which  shifted  the  debouch- 
ure southward  nearly  one-half  mile  from  its  present  position  (see 
Fig.  2i),  or  opposite  the  foot  of  Madison  street.  The  Calumet 
river  has  undergone  similar  changes  (see  Figs.  22  and  23).  That 
part  of  the  stream  east  of  Hegewisch  (Fig.  23)  has  been  reversed 
by  the  dredging  of  a  channel  from  Hegewisch  to  the  outlet  of  Lake 
Calumet. 


•J4.     Dune  near  Ouni'  Faik.    (Cowles.) 


CHICAGO  AND  ITS  ENVIRONS. 


59 


Some  years  ago  Dr.  Edmund  Andrews'  discussed  the  present 
beach  of  Lake  Michigan,  and  compared  its  strength  with  that  of 
the  beaches  of  Lake  Chicago.  His  paper  is  now  out  of  print,  but 
the  computations  have  been  reproduced  and  supplemented  by  Mr. 
Leverett  in  his  paper  already  referred  to.  The  computations  were 
made  for  the  purpose  of  obtaining  a  measure  of  post-glacial  time, 
from   the   rate  of   shore  erosion   to  the   north,  the   rate  of    littoral 


*^k-.  "  — ^.  ^a 

/W 

l»^ 

■^™^  T' 

_^^^^-r*«-=«^^^''^^^^'               ,..-             ..       , 

Fig.  25.     A  dune  in  process  of  destruction.    Sand  has  been  Ijlown  away,  except  where  lield  by 
the  roots  of  the  trees.     (Cowles.)     See  also  Fig.  28. 

transportation  to  the  south,  and  the  amount  of  filling  already  ac- 
complished since  the  withdrawal  of  the  ice.  While  there  are  many 
unknown  and  undeterminable  factors  in  such  a  problem,  the 
results  were,  as  Dr.  Andrews  remarked,  useful  in  showing  that  it 
is  impossible  to  allow,  even  on  the  most  liberal  estimates,  any  such 
duration  of  post-glacial  time  as  100,000  years,  which,  at  that  time, 
had  often  been  claimed. 


iThe    North    American    Lalces  Considered    as    Chronometers    of    Post-Glacial    Time. 
Edmund  Andrews,  M.D.,  Trans.  Chi.  Acad.  Sci.,  Vol.  II,  1870,  pp.  1-23. 


6o 


THE  (JEOGK.U'HY  OF 


The  dunes. — The  formation  of  sand  dunes  by  the  blowing  up 
of  the  fine  sand  from  the  beach  into  ridges  and  hills  has  been 
going  on,  perhaps  since  the  birth  of  Lake  Chicago;  but  the  most 
striking  results  have  been  accomplished  since  the  shore  of  the 
lake  reached  approximately  its  present  position.  Small  dunes, 
but  dunes  which  illustrate  all  essential  principles  of  dune  forma- 
tion, may  be  seen  at  Windsor  Park,  near  the  foot  of  Seventy-ninth 
street.  At  Dune  Park  and  Millers,  dunes  are  to  be  seen  in  all 
stages  of  development,  from  the  little  drifts  of  sand  in  the  lee  of 
stumps  or  shrubs,  to  great  shifting  hills  of  sand  loo  to  200  feet  in 
height.  The  position  of  the  more  important  dune€  about  Chicago 
is  indicated  on  Plate  II  (p.  8). 

The  formation  of  the  dunes  is  easily  understood.  As  the 
brisk  wind  which  is  carrying  sand  passes  an  obstructing  object, 
such  as  a  tree,  a  shrub,  or  a  tuft  of  grass,  its  current  is  inter- 
rupted, and  in  tlie  quieter  area  in    the  lee    of  the  obstruction  some 


Fig.  26.  Dune  covered  wiili  vegctatiun  in  the  backjrround.  Fresh  dune  in  tiie  foreground  to 
the  loft.  This  dune  is  migrating  toward  the  forest,  and  will  bury  it,  if  the  advance 
continues.    (Cowles.) 


CHICAGO  AND  ITS  ENVIRONS.  6l 

of  the  sand  is  dropped.  A  little  pile  or  drift  of  sand  accumulat- 
ing in  such  a  position  is  the  beginning  of  a  dune.  Hundreds  of 
them  may  be  seen  along  the  shore  at  the  present  time.  Where  a 
drift  of  sand  becomes  appreciable,  it  itself  becomes  an  obstruction, 
against  and  beyond  which  more  sand  lodges.  Thus  the  dune 
grows,  and  under  favorable  conditions  may  attain  great  dimensions 
(Fig  24). 


Fig.  27.    Trees  discovered  after  burial. >     In  the  background- to  the  right  are  hving  trees  which 
have  grown  since  the  present  surface  was  established.    (Cowies.) 

But  destruction  goes  hand  in  hand  with  construction  (Fig.  25). 
The  wind  takes  up  sand  not  only  from  the  beach,  but  from  the 
surface  of  the  dunes.  It  is  gathered  up  from  the  windward  side,  and 
carried  up  over  the  crest  only  to  be  dropped  on  the  leeward  slope. 
So  the  dune  may  be  shifted,  inch  by  inch,  from  windward  to  lee- 
ward. This  movement,  which  in  the  course  of  time  may  be  great, 
is  known  as  the  tnigration  of  dunes  (Fig.  26).  In  places  dunes  have 
moved  inland  great  distances,  burying  vegetation  and  devastating 

^For  an  excellent  discussion  of  the  vegetation  of  the  dunes,  see  articles  by  Dr.  Henry  C. 
Cowies  in  the  Botanical  Gazette,  Vol.  XXVII,  1898. 


62 


THE  GEOGRAPHY  OF 


fields.  Some  of  the  dunes  about  the  head  of  the  lake  are  now  far 
from  shore,  but  it  is  not  always  possible  to  say  how  far  their  posi- 
tion is  due  to  their  migration  inland,  and  how  far  to  the  recession 
of  the  shore  from  them,  as  the  result  of  shore-filling.  Dunes  are 
likely  to  be  migratory  until  vegetation  gets  a  foot-hold  on  them. 
When  this  is  done  the  sand  ceases  to  be  blown,  and  the  dune 
ceases  its  travels.  Thus  the  dunes  along  the  west  side  of  Blue 
Island  ridge,  and  between  Hammond  and  Thornton,  are  fixed, 
being  covered  and  held  by  vegetation,  while  the  dunes  about 
Millers  are  still  shifting. 


Fig.  2S.    Sand  which  once  buried  vegetation  has  been  blown  on,  exposing  the  dead  wood. 

After  a  dune  has  become  clothed  with  vegetation,  sand  may 
accumulate  upon  it,  being  lodged  by  the  shrubs  and  trees.  If  the 
sand  accumulates  more  rapidly  than  the  trees  grow  upward,  they 
will  be  buried.  This  has  been  done  at  various  points  about  the 
head  of  the  lake.  In  its  migration  the  moving  dune  may  bury 
trees  (Fig.  26).  If  the  sand  which  buries  the  forests  be  blown  on 
again  before  vegetation  gets  a  foot-hold  on  it,  the  dead  forest  may 
be  again  discovered, — resurrected,  but  not  to  life  (Fig.  27).      This 


CHICAGO  AND  ITS  ENVIRONS. 


63 


also  is  to  be  seen  about   the  head   of  the  lake  at   various  points 
near  Millers. 

Stream  erosion. — Stream  erosion  has  not  accomplished  much 
on  the  Chicago  plain  since  the  withdrawal  of  the  lake  waters  from 
it;  but  young  valleys  are  being  developed  in  the  highland  along 
the  lake  bluff  to  the  north  of  Evanston,  in  the  slopes  of  the  Blue 
Island  ridge,  in  Mount  Forest  Island,  in  the  sides  of  the  outlet, 
and  in  general  wherever  the  slopes  are  considerable.  Excellent 
examples  of  post-glacial  erosion  (young  valleys)  are  to  be  seen  in 
the  vicinity  of  Winnetka  and  Glencoe,  about  one  mile  west  of 
Palos  Springs,  and   at  various  points  along  the  outlet. 


Fig.  29.    Post-glacial  valleys,  shown  by  contours. 

The  trifling  amount  of  erosion  which  the  plain  itself  has  suf- 
fered is  to  be  seen  along  the  Chicago  river  (Fig.  30),  where  dredging 
has  not  been  carried  on,  along  the  Des  Plaines  river,  along  Salt 
creek  near  Riverside,  and  along  Thorn  creek.    The  small  amount  of 


Fig.  30.    Cross-section  of  the  Chicago  river  valley  near  Jefferson  Park. 

Stream  erosion,  the  poorly  developed  drainage,  the  lakes  and 
extensive  marshy  areas,  are  evidence  of  the  extreme  youth  of  the 
topography  of  the  area  under  discussion;  yet  it  is  to  be  remem- 
bered that  much  of  the  plain  is  too  low  for  stream  erosion  tobe 
effective. 


64       THE  GEOGKA/'I/y  OF  CHICAGO  AND  ITS  ENVIRONS. 

Weathering. — Since  the  glacial  drift  was  deposited,  perhaps 
6,000  to  10,000  years  ago,  it  has  been  changed  to  some  slight 
extent  by  weathering.  The  change  is  most  obvious  in  the  altera- 
tion of  color  which  its  surface  has  undergone.  While  the  body  of 
the  unstratified  drift  is  gray,  the  upper  part  just  beneath  the  soil  is 
huffish  or  brownish.  This  change  in  color  is  primarily  the  result 
of  oxidation  of  the  iron  compounds  originally  in  the  drift. 

The  formation  of  the  soil. — So  soon  as  the  ice  melted  from  the 
region,  weathering  began  to  prepare  the  surface  for  the  support  of 
plant  life.  When  vegetation  began  to  grow  and  die  and  decay, 
organic  matter  was  contributed  to  the  mineral  matter  which  sup- 
ported the  first  vegetation,  and  the  carbonaceous  matter  made  the 
soil  black.  The  same  changes  affected  the  area  temporarily  occu- 
pied by  the  lake,  so  soon  as  the  water  was  drawn  off.  The  growth 
of  the  vegetation  has,  in  turn,  furthered  the  surface  changes  in 
the  drift. 


UNIVERSfTY  OF  ILLINOIS-URBANA 


3  0112  079553720 


